Showing papers in "Science in 1978"
TL;DR: The commonly observed high diversity of trees in tropical rain forests and corals on tropical reefs is a nonequilibrium state which, if not disturbed further, will progress toward a low-diversity equilibrium community as mentioned in this paper.
Abstract: The commonly observed high diversity of trees in tropical rain forests and corals on tropical reefs is a nonequilibrium state which, if not disturbed further, will progress toward a low-diversity equilibrium community. This may not happen if gradual changes in climate favor different species. If equilibrium is reached, a lesser degree of diversity may be sustained by niche diversification or by a compensatory mortality that favors inferior competitors. However, tropical forests and reefs are subject to severe disturbances often enough that equilibrium may never be attained.
7,795 citations
TL;DR: The force required to separate two cells is shown to be greater than the expected electrical forces between cells, and of the same order of magnitude as the forces required to pull gangliosides and perhaps some integral membrane proteins out of the cell membrane.
Abstract: A theoretical framework is proposed for the analysis of adhesion between cells or of cells to surfaces when the adhesion is mediated by reversible bonds between specific molecules such as antigen and antibody, lectin and carbohydrate, or enzyme and substrate. From a knowledge of the reaction rates for reactants in solution and of their diffusion constants both in solution and on membranes, it is possible to estimate reaction rates for membrane-bound reactants. Two models are developed for predicting the rate of bond formation between cells and are compared with experiments. The force required to separate two cells is shown to be greater than the expected electrical forces between cells, and of the same order of magnitude as the forces required to pull gangliosides and perhaps some integral membrane proteins out of the cell membrane.
4,058 citations
TL;DR: The reactive superoxide radical, O2-, formerly of concern only to radiation chemists and radiobiologists, is now understood to be a normal product of the biological reduction of molecular oxygen.
Abstract: The reactive superoxide radical, O2-, formerly of concern only to radiation chemists and radiobiologists, is now understood to be a normal product of the biological reduction of molecular oxygen. An unusual family of enzymes, the superoxide dismutases, protect against the deleterious actions of this radical by catalyzing its dismutation to hydrogen peroxide plus oxygen.
3,273 citations
TL;DR: The initiation of continuous GnRH administration in animals with lesions and in which gonadotropin secretion is reestablished by intermittent GnRH replacement can result in a "desensitization" or "down regulation" of the processes responsible for gonadotropic hormone release.
Abstract: In rhesus monkeys with hypothalamic lesions that abolish gonadotropic hormone release by the pituitary gland, the constant infusion of exogenous gonadotropin-releasing hormone (GnRH) fails to restore sustained gonadotropin secretion. In marked contrast, intermittent administration of the synthetic decapeptide once per hour, the physiological frequency of gonadotropin release in the monkeys, reestablishes pituitary gonadotropin secretion. This phenomenon is attributable to the pattern of GnRH delivery rather than to the amounts of this hormone to which the cells of the pituitary are exposed. Moreover, the initiation of continuous GnRH administration in animals with lesions and in which gonadotropin secretion is reestablished by intermittent GnRH replacement can result in a "desensitization" or "down regulation" of the processes responsible for gonadotropin release.
1,226 citations
TL;DR: Observations suggest that many different classes of regulatory substances achieve certain of their biological effects by altering the phosphorylation of specific proteins.
Abstract: A variety of neurotransmitters, hormones, and other regulatory agents affect the phosphorylation of specific proteins in their target tissues. The types of stimuli that share this common effect on protein phosphorylation include numerous substances that do not act through cyclic AMP. These and other observations suggest that many different classes of regulatory substances achieve certain of their biological effects by altering the phosphorylation of specific proteins.
935 citations
TL;DR: By providing an integrated measurement of blood glucose, hemoglobin AIc is useful in assessing the degree of diabetic control and is a useful model of nonenzymatic glycosylation of other proteins that may be involved in the long-term complications of the disease.
Abstract: Glucose reacts nonenzymatically with the NH2-terminal amino acid of the beta chain of human hemoglobin by way of a ketoamine linkage, resulting in the formation of hemoglobin AIc. Other minor components appear to be adducts of glucose 6-phosphate and fructose 1,6-diphosphate. These hemoglobins are formed slowly and continuously throughout the 120-day life-span of the red cell. There is a two- to threefold increase in hemoglobin AIc in the red cells of patients with diabetes mellitus. By providing an integrated measurement of blood glucose, hemoglobin AIc is useful in assessing the degree of diabetic control. Furthermore, this hemoglobin is a useful model of nonenzymatic glycosylation of other proteins that may be involved in the long-term complications of the disease.
924 citations
TL;DR: Biological organization may be viewed as consisting of two stages: biosynthesis and assembly; that is, as a first approximation it represents a search by each structural molecule for its state of lowest chemical potential.
Abstract: Biological organization may be viewed as consisting of two stages: biosynthesis and assembly. The assembly process is largely under thermodynamic control; that is, as a first approximation it represents a search by each structural molecule for its state of lowest chemical potential. The hydrophobic effect is a unique organizing force, based on repulsion by the solvent instead of attractive forces at the site of organization. It is responsible for assembly of membranes of cells and intracellular compartments, and the absence of strong attractive forces makes the membranes fluid and deformable. The spontaneous folding of proteins, however, involves directed polar bonds, leading to more rigid structures. Intercellular organization probably involves polar bonds between cell surface proteins.
876 citations
TL;DR: Competition between female kin for local limiting resources may explain a male-biased secondary sex ratio in the prosimian Galago crassicaudatus, and data demonstrating the skewed sex ratio are presented.
Abstract: Competition between female kin for local limiting resources may explain a male-biased secondary sex ratio in the prosimian Galago crassicaudatus. Data demonstrating the skewed sex ratio, a brief summary of field observations on the species, and a simple mathematical statement of the hypothesis are presented. Local resource competition may influence sex ratio in other mammals.
868 citations
TL;DR: It is shown that nonequilibrium may become a source of order and that irreversible processes may lead to a new type of dynamic states of matter called "dissipative structures" and the thermodynamic theory of such structures is outlined.
Abstract: Fundamental conceptual problems that arise from the macroscopic and microscopic aspects of the second law of thermodynamics are considered. It is shown that nonequilibrium may become a source of order and that irreversible processes may lead to a new type of dynamic states of matter called "dissipative structures." The thermodynamic theory of such structures is outlined. A microscopic definition of irreversible processes is given, and a transformation theory is developed that allows one to introduce nonunitary equations of motion that explicitly display irreversibility and approach to thermodynamic equilibrium. The work of the group at the University of Brussels in these fields is briefly reviewed. In this new development of theoretical chemistry and physics, it is likely that thermodynamic concepts will play an ever-increasing role.
864 citations
TL;DR: Liposomes can be designed to release an entrapped drug preferentially at temperatures attainable by mild local hyperthermia, suggesting possible applications in the treatment of tumors or local infection.
Abstract: Liposomes can be designed to release an entrapped drug preferentially at temperatures attainable by mild local hyperthermia. In a test system in vitro, protein synthesis by Escherichia coli is inhibited and killing of the cells is enhanced by heating neomycin-containing liposomes to their phase transition temperature to maximize drug release. In the presence of serum the ratio of release at 44 degrees C to that at 37 degrees C can be made greater than 100:1, suggesting possible applications in the treatment of tumors or local infection.
TL;DR: Although rats without theta rhythm could not find their way directly to the goal, they recognized its location when they came upon it by chance, indicating a type of spatial deficit similar to that shown by hippocampally lesioned patient H.M.
Abstract: Rats learned, using distal room cues, to run to a goal on an elevated, circular track starting from any position on the track. The goal was one of eight equidistant, recessed cups set around the track, the goal cup being distinguished from the others solely by its position in the room. After learning, electrolytic lesions were made in the medial septal nucleus eliminating hippocampal theta rhythm in some animals but not in others. Rats without theta rhythm were no longer able to perform the spatial task, whereas rats with undisturbed theta rhythm retrained normal performance. Although rats without theta rhythm could not find their way directly to the goal, they recognized its location when they came upon it by chance. This type of spatial deficit appears similar to that shown by hippocampally lesioned patient H.M. Subsequent tests demonstrated that rats deprived of theta rhythm before training could nevertheless learn the task.
TL;DR: The nucleotide sequence of SV40 DNA was determined, and the sequence was correlated with known genes of the virus and with the structure of viral messenger RNA's.
Abstract: The nucleotide sequence of SV40 DNA was determined, and the sequence was correlated with known genes of the virus and with the structure of viral messenger RNA9s. There is a limited overlap of the coding regions for structural proteins and a complex pattern of leader sequences at the 59 end of late messenger RNA. The sequence of the early region is consistent with recent proposals that the large early polypeptide of SV40 is encoded in noncontinguous segments of DNA.
TL;DR: Anatomical asymmetries may help to explain the range of human talents, recovery from acquired disorders of language function, certain childhood learning disabilities, some dementing illnesses of middle life, and the evidence for behavioral lateralization in nonhuman primates.
Abstract: Structural asymmetries between the hemispheres are found in the human brain. Asymmetries in the auditory regions and in the Sylvian fissures are present even in the fetus. The Sylvian asymmetries may have existed in Neanderthal man and are found consistently in some apes. They may relate to right-left differences infunction. Thus, the striking auditory asymmetries could underlie language lateralization. The asymmetries in the frontal and occipital lobes and the lateral ventricles are correlated with hand preference. Anatomical asymmetries may help to explain the range of human talents, recovery from acquired disorders of language function, certain childhood learning disabilities, some dementing illnesses of middle life, and the evidence for behavioral lateralization in nonhuman primates.
TL;DR: It has been possible to determine the mean age of sediment provenances, as studies of sedimentary rocks suggest that the samarium-neodymium isotopic system is not substantially disturbed during sedimentation or diagenesis.
Abstract: Samarium-neodymium and rubidium-strontium isotopic systematics together with plausible assumptions regarding the geochemical evlution of continental crust material, have been used to ascertain the times at which segments of continental crust were formed. Analyses of composites from the Canadian Shield representing portions of the Superior, Slave, and Churchill structural provinces indicate that these provinces were all formed within the period 2.5 to 2.7 aeons. It has been possible to determine the mean age of sediment provenances, as studies of sedimentary rocks suggest that the samarium-neodymium isotopic system is not substantially disturbed during sedimentation or diagenesis.
TL;DR: In simulated atmospheres containing 1 part per million nitrogen dioxide and traces of nitric acid, directly mutagenic nitro derivatives are readily formed from both benzo[a]pyrene and perylene, a non-mutagen in the Ames reversion assay.
Abstract: Directly active mutagens are formed on exposure of the promutagen benzo[a]pyrene to gaseous pollutants in smog. In simulated atmospheres containing 1 part per million nitrogen dioxide and traces of nitric acid, directly mutagenic nitro derivatives are readily formed from both benzo[a]pyrene and perylene, a non-mutagen in the Ames reversion assay. Possible formation of direct mutagens by such reactions on sample collection filters, in exhaust effluents, and in the atmosphere should be recognized.
TL;DR: All factors that lower the oxygen affinity of hemoglobin act by strengthening the salt bridges that constrain its quaternary deoxy (T) structure.
Abstract: Electrostatic effects dominate many aspects of protein behavior. When polypeptide chains fold up, most polar side chains seek the exterior, where they can be solvated. Water bound in the interior has been found between the domains of enzymes of the chymotrypsin family, and between the subunits of hemoglobin and tobacco mosaic virus protein. Assembly of this protein from disk to virus is triggered by electrostatic interactions between neighboring subunits. Lysozyme stabilizes the constellation of charges involved in the transition state of its substrate by both permanent and induced dipoles. All factors that lower the oxygen affinity of hemoglobin act by strengthening the salt bridges that constrain its quaternary deoxy (T) structure. Enzymes of thermophile bacteria owe their extra stability mostly to additional salt bridges. The rate of denaturation of hemoglobins by alkali is determined by the ionization of internal side chains with pK9s of about 12.
TL;DR: The dopamine receptor blocker pimozide attenuated lever-pressing and running for food reward in hungry rats and appears to selectively blunt the rewarding impact of food and other hedonic stimuli.
Abstract: The dopamine receptor blocker pimozide attenuated lever-pressing and running for food reward in hungry rats. In each case the characteristic behavior of pimozide-treated rats was the same as that of undrugged rats when reward was simply withheld. Drug-induced performance difficulties were ruled out by the presence of periods of normal responding in drug-treated animals. Pimozide appears to selectively blunt the rewarding impact of food and other hedonic stimuli.
TL;DR: Synthetic maps constructed for Europe and the Near East show clines in remarkable agreement with those expected on the basis of the spread of early farming in Europe, supporting the hypothesis that this spread was a demic spread rather than a cultural diffusion of farming technology.
Abstract: Multivarate techniques can be used to condense the information for a large number of loci and alleles into one or a few synthetic variables. The geographic distribution of synthetic variables can be plotted by the same technique used in mapping the gene frequency of a single allele. Synthetic maps were constructed for Europe and the Near East, with the use of principal components to condense the information of 38 independent alleles from ten loci. The first principal component summarizes close to 30% of the total information and shows gradients. Maps thus constructed show clines in remarkable agreement with those expected on the basis of the spread of early farming in Europe, thus supporting the hypothesis that this spread was a demic spread rather than a cultural diffusion of farming technology.
TL;DR: The article reviews the developments that led to the involvement of the federal government in this activity through its sponsorship of professional standards review organizations (PSRO) and the major features of the PSRO's are described and their possible effects discussed.
Abstract: This article classifies the major approaches to the assessment of the process and outcomes of medical care. The apparent need to safeguard and enhance the quality of care has led to the institution of mechanisms that subject care to constant review so that deficiencies may be found and corrected. The article reviews the developments that led to the involvement of the federal government in this activity through its sponsorship of professional standards review organizations (PSRO's). The major features of the PSRO's are described and their possible effects discussed. It is too early to say how the PSRO's will fare, but should they fail to accomplish their objectives the pressure for more radical solutions will be difficult to resist.
TL;DR: The ability of oxygenated sterols to inhibit sterol synthesis in cultured cells and the ineffectiveness of cholesterol under the same conditions suggest that feedback regulation of sterol biosynthesis may be brought about by an oxygenated steroid rather than by cholesterol.
Abstract: A group of oxygenated sterols has been identified as potent and specific inhibitors of sterol biosynthesis. The ability of these compounds to inhibit sterol synthesis in cultured cells and the ineffectiveness of cholesterol under the same conditions suggest that feedback regulation of sterol biosynthesis may be brought about by an oxygenated sterol rather than by cholesterol. The nature of the regulatory sterol may vary in different cells with their specific requirements for cholesterol as a structural component or as a precursor of other steroid products. The use of oxygenated sterols to block sterol synthesis in cultured cells provides new information regarding the role of sterol in cell membrane structure and function. For example, de novo sterol synthesis is required for DNA synthesis and cell division by some cultured cells. Studies with cultured cells, and with rats and mice in vivo, suggest that oxygenated sterols could be of value in the treatment of several important human diseases.
TL;DR: Chicks whose vision was restricted to the frontal visual field became extremely myopic and had eyes of increased axial length and animals restricted to lateral field vision did not differ from normal animals.
Abstract: Chicks whose vision was restricted to the frontal visual field became extremely myopic (mean, -10 diopters; maximum, -24 diopters) and had eyes of increased axial length. Animals restricted to lateral field vision did not differ from normal animals. Monocular deprivation of form vision also produced myopia and eye enlargement and, in addition, produced increased anterior chamber depth.
TL;DR: The analysis shows through convergent lines of evidence that the biota is not a sink and may be a source of CO/sub 2/ as large or larger than the fossil fuel source.
Abstract: Current knowledge of the world carbon budget is reviewed with special emphasis on the question of whether the biota is a source or a sink for CO/sub 2/. The analysis shows through convergent lines of evidence that the biota is not a sink and may be a source of CO/sub 2/ as large or larger than the fossil fuel source. The issue is important because of the potential that changes in the CO/sub 2/ content of air have for changing climate worldwide. Various analyses suggest that human activities in the near future could release large additional amounts of CO/sub 2/ into the atmosphere with results that are substantially unpredictable.
TL;DR: Under depolarizing voltage clamp of Paramecium an inward calcium current developed and subsequently relaxed within 10 milliseconds, and inactivation of the calcium channel persisted after a pulse, as manifested by a reduced calcium current during subsequent depolarization.
Abstract: Under depolarizing voltage clamp of Paramecium an inward calcium current developed and subsequently relaxed within 10 milliseconds. The relaxation was substantially slowed when most of the extracellular calcium was replaced by either strontium or barium. Evidence is presented that the relaxation is not accounted for by a drop in electromotive force acting on calcium, or by activation of a delayed potassium current. Relaxation of the current must, therefore, result from an inactivation of the calcium channel. This inactivation persisted after a pulse, as manifested by a reduced calcium current during subsequent depolarization. Inactivation was retarded by procedures that reduce net entry of calcium, and was independent of membrane potential. The calcium channel undergoes inactivation as a consequence of calcium entry during depolarization. In this respect, inactivation of the calcium channel departs qualitatively from the behavior described in the Hodgkin-Huxley model of the sodium channel.
TL;DR: A permanent human cell line that maintains the granulocytic characteristics of acute myelogenous leukemia cells has been established and the cells of this line form myeloid colonies in soft gel culture in the presence of human colony-stimulating activity.
Abstract: A permanent human cell line that maintains the granulocytic characteristics of acute myelogenous leukemia cells has been established. The cells of this line form myeloid colonies in soft gel culture in the presence of human colony-stimulating activity. The cell line may be useful for studying human acute myelogenous leukemia and the mechanism of response to colony-stimulating activity.
TL;DR: "poor" performers were more vulnerable to both the enhancing effect of cholinergic agonist and precursor and the impairment after Cholinergic antagonist than "good" performers.
Abstract: Arecholine (4 milligrams), a cholinergic agonist, and choline (10 grams), a precursor of acetylcholine, significantly enhanced serial learning in normal human subjects. The subjects received methscopolamine prior to both arecholine and placebo injections. Conversely, scopolamine (0.5 milligram), a cholinergic antagonist, impaired learning and this impairment was reversed by arecholine and choline and the impairment after scopolamine were inversely proportional to the subject's performance on placebo; that is, "poor" performers were more vulnerable to both the enhancing effect of cholinergic agonist and precursor and the impairment after cholinergic antagonist than "good" performers.
TL;DR: The symbiotic theory of cellular evolution is considered the most probable because it holds that organelles, e.g., mitochondria and chloroplasts invaded larger bodies, and combined functions to form eucaryotic cells.
Abstract: A computer branching model is used to analyze cellular evolution. Attention is given to certain key amino acids and nucleotide residues (ferredoxin, 5s ribosomal RNA, and c-type cytochromes) because of their commonality over a wide variety of cell types. Each amino acid or nucleotide residue is a sequence in an inherited biological trait; and the branching method is employed to align sequences so that changes reflect substitution of one residue for another. Based on the computer analysis, the symbiotic theory of cellular evolution is considered the most probable. This theory holds that organelles, e.g., mitochondria and chloroplasts invaded larger bodies, e.g., bacteria, and combined functions to form eucaryotic cells.
TL;DR: The findings are consistent with recent hypotheses that endocrine levels are related to brain aging, either as cause or effect.
Abstract: Altered neural-endocrine relations have been proposed as factors in mammalian aging. In the same rats from three age groups we quantified astrocyte reactivity in hippocampus, performed radioimmunoassays for plasma adrenocorticoids, and measured adrenal weight. These variables were correlated in individual animals and generally increased with age. The findings are consistent with recent hypotheses that endocrine levels are related to brain aging, either as cause or effect.
TL;DR: Prednisone treatment for infertility and subsequent pregnancy maintenance in humans resulted in a significant decrease in the birth weight of full-term infants and a marked increase in the percentage of newborn infants weighing 2500 grams or less, that is, "light for dates" in comparison to control offspring.
Abstract: Prednisone treatment for infertility and subsequent pregnancy maintenance in humans resulted in a significant decrease in the birth weight of full-term infants and a marked increase in the percentage of newborn infants weighing 2500 grams or less, that is, "light for dates" in comparison to control offspring. A parallel experiment with mice indicated that the reduction of birth weight was caused by exposure to corticosteroids rather than to maternal disease or malfunction.
TL;DR: This article proposes a modification of the currently accepted view of the central neural integration of body temperature, in place of a single integrator with multiple inputs and outputs, which includes as many integrators as there are thermoregulatory responses.
Abstract: This article proposes a modification of the currently accepted view of the central neural integration of body temperature In place of a single integrator with multiple inputs and outputs, the new model includes as many integrators as there are thermoregulatory responses Futhermore, these integrators are postulated to be represented at many levels of the nervous system, with each level facilitated or inhibited by levels above and below The purpose of such a complicated arrangement is to achieve finer and finer control over body temperature A consideration of how endothermy might have evolved, with originally nonthermally related responses gradually coming under thermal control, makes such a brain organization highly reasonable