Showing papers in "Proceedings of the National Academy of Sciences of the United States of America in 1971"
TL;DR: The hypothesis is developed that retinoblastoma is a cancer caused by two mutational events, in the dominantly inherited form, one mutation is inherited via the germinal cells and the second occurs in somatic cells.
Abstract: Based upon observations on 48 cases of retinoblastoma and published reports, the hypothesis is developed that retinoblastoma is a cancer caused by two mutational events. In the dominantly inherited form, one mutation is inherited via the germinal cells and the second occurs in somatic cells. In the nonhereditary form, both mutations occur in somatic cells. The second mutation produces an average of three retinoblastomas per individual inheriting the first mutation. Using Poisson statistics, one can calculate that this number (three) can explain the occasional gene carrier who gets no tumor, those who develop only unilateral tumors, and those who develop bilateral tumors, as well as explaining instances of multiple tumors in one eye. This value for the mean number of tumors occurring in genetic carriers may be used to estimate the mutation rate for each mutation. The germinal and somatic rates for the first, and the somatic rate for the second, mutation, are approximately equal. The germinal mutation may arise in some instances from a delayed mutation.
7,051 citations
TL;DR: Three mutants have been isolated in which the normal 24-hour rhythm is drastically changed and all these mutations appear to involve the same functional gene on the X chromosome.
Abstract: Three mutants have been isolated in which the normal 24-hour rhythm is drastically changed. One mutant is arrhythmic; another has a period of 19 hr; a third has a period of 28 hr. Both the eclosion rhythm of a population and the locomotor activity of individual flies are affected. All these mutations appear to involve the same functional gene on the X chromosome.
2,161 citations
TL;DR: This action of dimethyl sulfoxide, which was reversible, may represent the derepression of leukemic cells to permit their maturation in cloned line of murine virus-induced erythroleukemia.
Abstract: Cells of a cloned line of murine virus-induced erythroleukemia were stimulated to differentiate along the erythroid pathway by dimethyl sulfoxide at concentrations that did not inhibit growth. A rise in the number of benzidine-positive normoblasts was accompanied by increased synthesis of heme and hemoglobin and a decrease in the malignancy of the cells. This action of dimethyl sulfoxide, which was reversible, may represent the derepression of leukemic cells to permit their maturation.
1,175 citations
TL;DR: Aerotolerant anaerobes, which survive exposure to air and metabolize oxygen to a limited extent but do not contain cytochrome systems, were found to be devoid of catalase activity but did exhibit superoxide dismutase activity.
Abstract: The distribution of catalase and superoxide dismutase has been examined in various micro-organisms. Strict anaerobes exhibited no superoxide dismutase and, generally, no catalase activity. All aerobic organisms containing cytochrome systems were found to contain both superoxide dismutase and catalase. Aerotolerant anaerobes, which survive exposure to air and metabolize oxygen to a limited extent but do not contain cytochrome systems, were found to be devoid of catalase activity but did exhibit superoxide dismutase activity. This distribution is consistent with the proposal that the prime physiological function of superoxide dismutase is protection of oxygen-metabolizing organisms against the potentially detrimental effects of the superoxide free radical, a biologically produced intermediate resulting from the univalent reduction of molecular oxygen.
974 citations
TL;DR: Tests of the convolution method with computer-simulated shadowgraphs show that it is also more accurate than the Fourier transform method, and has good potentialities for application in electron microscopy and x-radiography.
Abstract: A new technique is proposed for the mathematical process of reconstruction of a three-dimensional object from its transmission shadowgraphs; it uses convolutions with functions defined in the real space of the object, without using Fourier transforms. The object is rotated about an axis at right angles to the direction of a parallel beam of radiation, and sections of it normal to the axis are reconstructed from data obtained by scanning the corresponding linear strips in the shadowgraphs at different angular settings.
Since the formulae in the convolution method involve only summations over one variable at a time, while a two-dimensional reconstruction with the Fourier transform technique requires double summations, the convolution method is much faster (typically by a factor of 30); the relative increase in speed is larger where greater resolution is required. Tests of the convolution method with computer-simulated shadowgraphs show that it is also more accurate than the Fourier transform method. It has good potentialities for application in electron microscopy and x-radiography. A new method of reconstructing helical structures by this technique is also suggested.
967 citations
TL;DR: By this technique, the composition of body fluids can be made constant after a few days, permitting significant quantitative analyses to be performed, and should be useful in the application of the principles of orthomolecular medicine.
Abstract: When a human being is placed for several days on a completely defined diet, consisting almost entirely of small molecules that are absorbed from the stomach into the blood, intestinal flora disappear because of lack of nutrition. By this technique, the composition of body fluids can be made constant (standard deviation about 10%) after a few days, permitting significant quantitative analyses to be performed. A method of temperature-programmed gas-liquid partition chromatography has been developed for this purpose. It permits the quantitative determination of about 250 substances in a sample of breath, and of about 280 substances in a sample of urine vapor. The technique should be useful in the application of the principles of orthomolecular medicine.
925 citations
TL;DR: It is pointed out that translational and (overall) rotational motions provide the important entropic driving force for enzymic and intramolecular rate accelerations and the chelate effect; internal rotations and unusually severe orientational requirements are generally of secondary importance.
Abstract: It is pointed out that translational and (overall) rotational motions provide the important entropic driving force for enzymic and intramolecular rate accelerations and the chelate effect; internal rotations and unusually severe orientational requirements are generally of secondary importance. The loss of translational and (overall) rotational entropy for 2 → 1 reactions in solution is ordinarily on the order of 45 entropy units (e.u.) (standard state 1 M, 25°C); the translational entropy is much larger than 8 e.u. (corresponding to 55 M). Low-frequency motions in products and transition states, about 17 e.u. for cyclopentadiene dimerization, partially compensate for this loss, but “effective concentrations” on the order of 108 M may be accounted for without the introduction of new chemical concepts or terms.
915 citations
TL;DR: A model is developed for the coexistence and exclusion of species over a region of similar habitable patches since the balance of local extinction and colonization would leave some patches unoccupied even without competitors.
Abstract: A model is developed for the coexistence and exclusion of species over a region of similar habitable patches. Since the balance of local extinction and colonization would leave some patches unoccupied even without competitors, species may coexist even when all the patches are the same. Regional competition coefficients are found when species affect the local extinction or migration rates of each other. Rare species can regulate each other and even exclude other species completely.
732 citations
TL;DR: The concentration of prolactin in the serum of normal children and adults of either sex was usually below 30 ng/ml, while very high concentrations were observed in newborn infants, and during pregnancy, the concentration rose progressively from an average of 30 ng-ml in the first trimester to 200 ng-ML at term.
Abstract: A radioimmunoassay for primate prolactin has been developed, with [(131)I] monkey prolactin, and antibodies to monkey or human prolactin. The assay is specific for prolactin; human growth hormone, and human and monkey placental lactogen show no significant crossreaction. The assay is sensitive enough to measure prolactin concentrations in the sera of most humans studied. The concentration of prolactin in the serum of normal children and adults of either sex was usually below 30 ng/ml, while very high concentrations (up to 500 ng/ml) were observed in newborn infants. The serum prolactin concentration during the menstrual cycle showed no definite increase in the luteal phase. Of 24 patients with galactorrhea, 20 had prolactin concentrations above 30 ng/ml; the highest value observed was 1500 ng/ml. In contrast, 12 of 13 patients with acromegaly had concentrations within the normal range. During pregnancy, the concentration of prolactin in serum rose progressively from an average of 30 ng/ml in the first trimester to 200 ng/ml at term. Postpartum, prolactin concentrations fell to normal levels after 1-2 weeks. Suckling was a potent stimulus to prolactin release, increasing its concentration in serum some 10- to 20-fold.
730 citations
TL;DR: The authors' evidence supports the hypothesis that the propagated bending waves of live-sperm tails are the result of ATP-induced shearing forces between outer tubules which, when resisted by the native structure, lead to localized sliding and generate an active bending moment.
Abstract: Axonemes isolated from the sperm of the sea urchin, Tripneustes gratilla, were briefly digested with trypsin. The digested axonemes retained their typical structure of a cylinder of nine doublet-tubules surrounding a pair of single tubules. The digestion modified the axonemes so that the subsequent addition of 0.1 mM ATP caused them to disintegrate actively into individual tubules and groups. The nucleotide specificity and divalent-cation requirements of this disintegration reaction paralleled those of flagellar motility, suggesting that the underlying mechanisms were closely related. Observations by dark-field microscopy showed that the disintegration resulted from active sliding between groups of the outer doublet-tubules, together with a tendency for the partially disintegrated axoneme to coil into a helix. Our evidence supports the hypothesis that the propagated bending waves of live-sperm tails are the result of ATP-induced shearing forces between outer tubules which, when resisted by the native structure, lead to localized sliding and generate an active bending moment.
672 citations
TL;DR: It is suggested that the blocking factor in sera from tumor-bearing animals is an antigen-antibody complex, capable of binding to the target cells and/or reacting with lymphocytes immune to their antigens, thus blocking the lymphocytes' reactivity.
Abstract: Sera from mice carrying progressively growing sarcomas induced by Moloney virus or methylcholanthrene can block the cytotoxic effect of lymphocytes immune to the tumor-specific antigens of the respective neoplasms. The blocking effect can be specifically removed by absorbing sera with the respective types of tumor cells, and it can be recovered from these cells by elution at low pH. If the low pH is maintained, it is possible to separate out a low and a high molecular weight fraction from the eluates. If the fractions are added to the target cells for 45 minutes and then removed, neither of these fractions can block lymphocyte-mediated cytotoxicity, while a 1:1 mixture of them has a specific blocking effect. If they are admixed with the lymphocytes, incubated for 1 hr, and then allowed to incubate with the target cells and lymphocytes during the entire 2 days of the test, the low molecular weight fraction, as well as the mixture, but not the high molecular weight fraction, has a blocking activity. It is suggested that the blocking factor in sera from tumor-bearing animals, as regularly tested, is an antigen-antibody complex, capable of binding to the target cells and/or reacting with lymphocytes immune to their antigens, thus blocking the lymphocytes' reactivity; the latter reaction is postulated to be of a temporary nature.
TL;DR: This study originated in response to questions that arise in the study of supercoiled double-stranded DNA rings, and measures the extent to which coiling of the central curve has relieved local twisting of the cord.
Abstract: A geometric invariant of a space curve, the writhing number, is defined and studied. For the central curve of a twisted cord the writhing number measures the extent to which coiling of the central curve has relieved local twisting of the cord. This study originated in response to questions that arise in the study of supercoiled double-stranded DNA rings.
TL;DR: If the additional conserved quantity is a convex function of the original ones, the original system can be put into symmetric hyperbolic form and an entropy inequality is derived.
Abstract: We discuss first-order systems of nonlinear conservation laws which have as a consequence an additional conservation law. We show that if the additional conserved quantity is a convex function of the original ones, the original system can be put into symmetric hyperbolic form. Next we derive an entropy inequality, which has also been suggested by I. Kružhkov, for discontinuous solutions of the given system of conservation laws.
TL;DR: Evidence is presented that the development of these colonies is under separate control from that of granulocytic colonies found in the same cultures.
Abstract: A culture method has been developed in which erythroid colonies are produced in vitro from hemopoietic cells from the livers of 13-day fetuses of C3Hf/Bi mice. Heme synthesis by the cultures was correlated with the presence of these colonies, and the hemoglobin produced was shown to be electrophoretically normal. The individual colonies were identified as erythroid since they were erythropoietin-dependent, positively stained by the histochemical “Lepehne” procedure for hemoglobin, and labeled by 59Fe radioautography. Evidence is presented that the development of these colonies is under separate control from that of granulocytic colonies found in the same cultures.
TL;DR: A lipophilic, left-handed helical structure is proposed for gramicidin A in which the C-O bonds alternately point toward the amino and carboxyl ends; it is a hybrid of the 4.314 and 4.416 helices.
Abstract: A lipophilic, left-handed helical structure is proposed for gramicidin A in which the C-O bonds alternately point toward the amino and carboxyl ends; it is a hybrid of the 4.314 and 4.416 helices. The C-O groups pointing toward the carboxyl end form part of 16-membered hydrogen-bonded rings, whereas the C-O moieties pointing toward the amino end form 14-membered hydrogenbonded rings. The proposed structure is based on conformational analysis combined with requirements for the gramicidin A transmembrane channel. Two helices combine to form the channel. The alternating C-O directions allow hydrogen-bonded dimerization by the unique possibilities of head-to-head and tail-to-tail attachment. The formyl group at the amino end allows for a favorable head-to-head attachment with no loss of structural continuity. Unpublished studies. by M. C. Goodall on the lipid bilayer conductance of deformyl gramicidin A strongly argue for head-to-head attachment. Such hydrogen-bonded association is not possible with previously described helices, as the C-O groups all point in the same direction. In relation to possible π(L,D) helices in mammalian systems, it should be noted that glycines would fill the role of D residues.
The conformation can undergo ion-induced relaxations, which provide approximate tetrahedral coordination for the ion, with facile shifting of coordinations. The ready exchange of coordinations provides the mechanism for movement of the ion along the channel. Conceivably, such transmembrane channels could have application as models for ion transport across biological membranes—an application which may be as great as, or greater than, that of carriers such as valinomycin and nonactin. Specifically, biogenic amines and drugs containing aromatic groups could control access to the channel by interactions with the two tryptophan residues at the ethanolamine end and with the negative region provided by the three oxygens.
TL;DR: Preliminary data indicate that the protein is unique to sarcoplasmic reticulum and that it is hydrophobically bonded on the interior of these vesicles, and the name Calsequestrin is suggested for the protein.
Abstract: An acidic protein has been extracted from sarcoplasmic reticulum with KCl and deoxycholate. The protein, which remains soluble after extraction, has been highly purified by fractionation on DEAE-cellulose, Sephadex, and hydroxylaptite. It has a molecular weight of 44,000 and contains 392 amino acid residues per molecule, of which 146 are either glutamic or aspartic acid. No phosphorus, sialic acid, or lipid has been detected in the preparation. The protein has been shown to bind up to 970 nmol of Ca++ per mg (43 mol/mol) at pH 7.5, with an apparent dissociation constant of 4 × 10-5 M. Preliminary data indicate that the protein is unique to sarcoplasmic reticulum and that it is hydrophobically bonded on the interior of these vesicles. The protein is believed to play a role in sequestering calcium within sarcoplasmic reticulum. The name Calsequestrin is suggested for the protein.
TL;DR: Eight insulins and derivatives with biological potencies that differed over a 100-fold range inhibited the binding of insulin to liver membranes in direct proportion to their ability to stimulate glucose oxidation in isolated fat cells.
Abstract: With [125I]insulin at 7 × 10-10 M, 25% of the radioactivity was bound to plasma membranes purified from rat liver. 20% of the [125I]insulin binding was inhibited by unlabeled insulin at 10-9 M (6 ng/ml), equivalent to insulin concentrations in hepatic portal blood; inhibition of [125I]insulin binding was 80% at 10-7 M and 90% at 10-5 M. Eight insulins and derivatives with biological potencies that differed over a 100-fold range inhibited the binding of [125I]insulin to liver membranes in direct proportion to their ability to stimulate glucose oxidation in isolated fat cells. Inactive insulin chains, as well as glucagon, ACTH, and human growth harmone were without effect. The binding of [125I]insulin increased 55-fold as plasma membrane was purified from crude homogenate. Binding was time- and temperature-dependent, and addition of excess insulin produced rapid dissociation of [125I]insulin. This study demonstrates directly the binding of insulin to its biologically important receptors.
TL;DR: Treatment of Chinese hamster ovary cells in vitro with dibutyrl adenosine cyclic 3':5'-monophosphate converts the culture from one of compact, randomly oriented cells that grow in multilayers to a monolayer of elongated, fibroblast-like cells growing parallel to one another.
Abstract: Treatment of Chinese hamster ovary cells in vitro with dibutyrl adenosine cyclic 3':5'-monophosphate converts the culture from one of compact, randomly oriented cells that grow in multilayers to a monolayer of elongated, fibroblast-like cells growing parallel to one another. Testosterone propionate, which has a similar though smaller effect at high concentrations and after prolonged incubation, potentiates the action of dibutyryl cyclic AMP even when added at very low concentrations. The transformation is recognizable within one hour, affects cells throughout all or most of the life cycle, and is completely reversible. Both cell forms can reproduce, with approximately the same generation time. Agents like colcemid and vinblastine, which inhibit assembly of microtubules, prevent the transformation to the fibroblast-like form. It is postulated that the dibutyryl cyclic AMP and testosterone act by promoting organization of microtubules from protein monomers.
TL;DR: Results are interpreted as evidence that the glial cell is involved in limiting the extracellular build-up of substances that might trigger synaptic transmission by removing any transmitters that may diffuse out of the synaptic cleft during the transmission of impulses.
Abstract: Rabbit-brain fractions enriched in neuronal cell bodies and in glial cells accumulated norepinephrine, serotonin, dopamine, and γ-aminobutyric acid, substances believed to serve as neurotransmitters in the central nervous system. Both neurons and glia were able to concentrate the monoamine transmitters about 4-fold from a medium containing 0.1-1 μM concentrations. However, the glial-cell fraction concentrated aminobutyrate over a 100-fold from the medium, in contrast to the neuronal fraction, which concentrated this amino acid only 4-fold. The uptake of aminobutyrate by glial cells was 30-50% of that of synaptosome preparations. Its uptake in all fractions was temperature sensitive, sensitive to metabolic inhibitors, and exhibited Km values of 0.72 μM for the neuronal fraction, 0.42 μM for the synaptosomal fraction, and 0.27 μM for the glial-cell fraction. These results are interpreted as evidence that the glial cell is involved in limiting the extracellular build-up of substances that might trigger synaptic transmission by removing any transmitters that may diffuse out of the synaptic cleft during the transmission of impulses. The possible function of the enormous ability of glia and synaptosomes to accumulate aminobutyrate is discussed in light of the actions and distribution of this substance in the central nervous system.
TL;DR: The rapidly-labeled polyribosomal RNA component from mouse sarcoma 180 cells is retained on nitrocellulose (Millipore) membrane-filters at high ionic strength due to the presence of a polynucleotide sequence rich in adenylic acid that resists both T(1) and pancreatic RNase digestion.
Abstract: The rapidly-labeled polyribosomal RNA component from mouse sarcoma 180 cells is retained on nitrocellulose (Millipore) membrane-filters at high ionic strength. This property is due to the presence of a polynucleotide sequence rich in adenylic acid that resists both T(1) and pancreatic RNase digestion. The resistant material shows sedimentation characteristics close to those of transfer RNA. The RNA molecules that contain this material can be separated from the rest of the polysomal RNA by differential phenol extraction with neutral and alkaline Tris buffers. Synthetic poly(A) exhibits the same behavior as the rapidly-labeled polysomal RNA with respect to Millipore binding and phenol fractionation. The characteristics of the rapidly-labeled polysomal RNA component permit its isolation free of ribosomal RNA.
TL;DR: Polyadenylate sequences have been found covalently linked in heterogeneous DNA-like nuclear RNA of HeLa cells, and a possible model for mRNA synthesis from large heterogeneous nuclear RNA precursor molecules is discussed.
Abstract: Polyadenylate sequences have been found covalently linked in heterogeneous DNA-like nuclear RNA of HeLa cells. This poly(A) material seems homogeneous in size and accounts for about 0.5% of such RNA. Similar poly(A) sequences were found in rapidly-labeled polyribosomal RNA, thought to be messenger RNA. A possible model for mRNA synthesis from large heterogeneous nuclear RNA precursor molecules is discussed.
TL;DR: A species of cytochrome b(5) with a monomer molecular weight of 16,700 has been isolated from rabbit-liver microsomes by a procedure that uses detergents and avoids the use of any proteolytic or lipolytic enzymes, and appears to contain an extremely hydrophobic appendage of 40 amino acids at the N-terminus.
Abstract: A species of cytochrome b5 with a monomer molecular weight of 16,700 has been isolated from rabbit-liver microsomes by a procedure that uses detergents and avoids the use of any proteolytic or lipolytic enzymes. This detergent-extracted cytochrome b5 is larger than the trypsin- or lipase-extracted enzyme, and appears to contain an extremely hydrophobic appendage of 40 amino acids, probably at the N-terminus. The hydrophobic character of the extra amino acid sequence leads to aggregation in the absence of detergents, and may be of considerable importance in the binding of the enzyme to microsomes. It is suggested that the hydrophilic portion of the cytochrome molecule, which bears the heme and is enzymatically functional, is oriented toward the surface of the membrane where it readily reacts with nonmicrosomal proteins, while the hydrophobic “tail” anchors the heme protein tightly to the membrane.
TL;DR: The results suggest that the production of 1,25-dihydroxycholecalciferol, believed to be the metabolically active form of vitamin D in the intestine, is responsible for the adaptation of calcium absorption to low dietary concentrations of calcium.
Abstract: Tritiated 1,25-dihydroxycholecalciferol accumulates in several tissues, to an extent that varies with dietary calcium content, 12 hr after the administration of 325 pmoles of tritiated 25-hydroxycholecalciferol to rats. As the dietary and serum calcium concentrations increase, the amount of 1,25-dihydroxycholecalciferol is diminished and the concentration of 21,25-dihydroxycholecalciferol increases. This correlation is especially evident in rats given vitamin D3. In vitamin D-deficient rats, the repression of 1,25-dihydroxycholecalciferol formation occurs with a diet containing 3% calcium and 20% lactose. The results suggest that the production of 1,25-dihydroxycholecalciferol, believed to be the metabolically active form of vitamin D in the intestine, is responsible for the adaptation of calcium absorption to low dietary concentrations of calcium.
TL;DR: The total binding capacity of fat cells is quantitatively recovered in the particulate fraction after homogenization, and the insulin-cell receptor interaction is a simple dissociable process involving a homogeneous species probably present exclusively in the cell membrane.
Abstract: An assay system is described for measurement of specific binding of [125I]insulin to intact fat cells and membrane fractions from such cells. The binding is time- and temperature-dependent and saturable with respect to insulin; the bound insulin is displaced by native insulin but not by oxidized or reduced insulin or by a number of other peptide hormones. A maximum of about 11,000 molecules of insulin can bind per cell. The insulin-receptor association is a bimolecular reaction with a rate constant of 1.5 × 107 M-1 sec-1, while the dissociation is a strictly first-order process with a rate constant of 7.4 × 10-4 sec-1. A dissociation constant of 5.0 × 10-11 M can be calculated from these rate constants, whereas a value of 6.1 × 10-11 M is obtained on the basis of enhancement of glucose oxidation. Complex formation does not result in chemical change or inactivation of insulin or receptor. The total binding capacity of fat cells is quantitatively recovered in the particulate fraction after homogenization. The insulin-cell receptor interaction is a simple dissociable process involving a homogeneous species probably present exclusively in the cell membrane.
TL;DR: The data suggest that cyclic AMP may be an important factor in the determination of morphology of normal fibroblasts and this function may be lost or altered during transformation.
Abstract: Sarcoma cells growing in tissue culture have morphological and growth characteristics different than normal fibroblasts. Several of the morphological characteristics of normal fibroblasts are regained when the cells are incubated with dibutyryl-cyclic AMP or butyryl-cyclic AMP (0.1-1 mM), or cyclic AMP (3 mM) plus theophylline (1 mM), but not with ATP, ADP, AMP, adenine, or adenosine (1-7 mM). The cell bodies become elongated; distinct narrow processes are formed. With prolonged incubation, the cells show less tendency to pile up or become polygonal. Further, L-929 and Rous sarcomatransformed hamster cells orient in parallel arrays characteristic of contact inhibition. The cells retain their altered morphology as long as the butyryl-cyclic AMP is present, but revert after its removal. Experiments with cycloheximide, puromycin, and actinomycin D indicate that protein Synthesis, but not RNA synthesis, is required for the response. Microtubular proteins may be involved. No response is observed with normal fibroblasts or with various epithelial cells. The data suggest that cyclic AMP may be an important factor in the determination of morphology of normal fibroblasts and this function may be lost or altered during transformation.
TL;DR: In mouse brain the stereospecific binding of levorphanol represents only 2% of the total association of drug with tissue, and it was found only in certain membrane fractions.
Abstract: A method is described for analyzing the association of the opiate narcotic levorphanol with brain tissue into three components: nonsaturable, saturable nonspecific, and saturable stereospecific. The method may be of general applicability for the study of the interaction of drugs with body tissues. In mouse brain the stereospecific binding of levorphanol represents only 2% of the total association of drug with tissue, and it was found only in certain membrane fractions. The material responsible for the stereospecific binding might be the opiate receptor.
TL;DR: Hepatic ribosomes have been dissociated into biologically active subunits as follows: polysomes were treated at 0 degrees C with puromycin at high ionic strength and heated to 37 degrees C, when they dissociated completely into subunits.
Abstract: Hepatic ribosomes have been dissociated into biologically active subunits as follows. Polysomes were treated at 0 degrees C with puromycin at high ionic strength. This released most of the nascent polypeptide chains without dissociating the polysomes, which retained the mRNA and the tRNA moiety of peptidyl tRNA, but were unable to continue the translation of mRNA. The polysomes were then heated to 37 degrees C, when they dissociated completely into subunits. Similar treatment without puromycin resulted in only partial dissociation.
TL;DR: The complete amino-acid sequence of the 2.5S nerve growth factor from male-mouse submaxillary glands has been determined and the alignment of the three disulfide bonds, determined from a combination of peptic and thermolytic digestions, is I-IV, II-V, and III-VI.
Abstract: The complete amino-acid sequence of the 2.5S nerve growth factor from male-mouse submaxillary glands has been determined. The unambiguous alignment of peptides derived from tryptic, chymotryptic, thermolytic, and peptic digestion of S-carboxymethyl-, S-aminoethyl-, and native growth factor indicates that the primary subunit is composed of 118 amino acids, with amino-terminal serine and carboxyl-terminal arginine. The molecular weight of this subunit, calculated from the primary sequence, is 13,259. Thus, the native protein, which is composed of two of the subunits, has a molecular weight of 26,518. These values, as well as the final amino-acid composition, are in excellent agreement with those determined by direct measurement with undigested growth factor. The alignment of the three disulfide bonds, determined from a combination of peptic and thermolytic digestions, is I-IV, II-V, and III-VI. The latter two pairs are located in a closed loop of 14 amino acids, by virtue of the fact that half-cystinyl residues V and VI are separated by only a single residue in the linear sequence. Assignment of the side-chain amides showed that 7 of 11 aspartic acid residues and 2 of 8 glutamic acid residues are present as amides. This distribution of charged residues is entirely consistent with the observed isoelectric point of 9.3.
TL;DR: It is proposed that these Compounds I contain a pi-cation radical of the heme prosthetic group, which explains the oxidation level, optical spectra, and stability of the primary compounds without recourse to properties such as stoichiometric mixtures of special porphyrins, stable Fe(V) porphyrs, or unique conformers of heme porphirins.
Abstract: Two-electron oxidation of cobaltous octaethylporphyrin [Co(II)(Et)8P] yields a stable π-cation radical [Co(III)(Et)8P]2+., the optical spectrum of which exhibits spectral changes dependent upon the nature of the counterion. Comparison of these spectra with those of Compounds I of horseradish peroxidase and catalase leads us to propose that these Compounds I contain a π-cation radical of the heme prosthetic group. This proposal explains the oxidation level, optical spectra, and stability of the primary compounds without recourse to properties such as stoichiometric mixtures of special porphyrins, stable Fe(V) porphyrins, or unique conformers of heme porphyrins. Explanations are advanced to account for the missing electron spin resonance signal of Compound I of horseradish peroxidase.
TL;DR: In the presence of over-threshold concentrations of simple neutral polymers and salts, DNA undergoes a cooperative change in its solution structure and collapses into particles approaching the compactness of the contents of phage heads.
Abstract: In the presence of over-threshold concentrations of simple neutral polymers and salts, DNA undergoes a cooperative change in its solution structure Sedimentation studies at low DNA concentrations show that phage DNA molecules collapse into particles approaching the compactness of the contents of phage heads The interaction between DNA and polymers is thought to be nonspecifically replusive