Showing papers by "University of Würzburg published in 1983"

Adoptive transfer of EAE-like lesions from rats with coronavirus-induced demyelinating encephalomyelitis

Abstract: Viruses have been found to induce inflammatory demyelinating lesions in central nervous system (CNS) tissue of both animal and man, either by natural infections or after vaccination. At least two different pathogenic mechanisms have been proposed for these changes, a cytopathic viral infection of oligodendroglia cells with subsequent cell death, and a host immune reaction against virus and brain antigens. We now report the occurrence of cell-mediated immune reactions against basic myelin proteins in the course of coronavirus infections in Lewis rats. Infection of rats with the murine coronavirus JHM leads to demyelinating encephalomyelitis developing several weeks to months postinfection. Lymphocytes from these diseased Lewis rats can be restimulated with basic myelin protein (BMP) and adoptive transfer of these cells leads to lesions resembling those of experimental allergic encephalomyelitis (EAE) in recipients, which can be accompanied by a mild clinical disease. This model demonstrates that a virus infection in CNS tissue is capable of initiating an autoimmune response which may be of pathogenic importance.

Cardiovascular Reflex Control by Afferent Fibers from Skeletal Muscle Receptors

Abstract: The sections in this article are: 1 Afferent Fibers from Skeletal Muscle and Their Receptors 1.1 Composition of Muscle Nerves 1.2 Muscle Spindles and Golgi Tendon Organs 1.3 Receptive Properties of Group III and Group IV Afferent Fibers 2 Central Pathways for Cardiovascular Reflexes from Skeletal Muscle Receptors 2.1 Spinal Termination of Primary Muscle Afferents 2.2 Central Pathways Arising From Myelinated Primary Muscle Afferents 2.3 Central Pathways Arising From Unmyelinated Primary Muscle Afferents 2.4 Ascending and Descending Spinal Pathways Involved in Cardiovascular Reflex Control From Skeletal Muscle 3 Organization of Efferent Outflow in Pre- and Postganglionic Neurons 4 Cardiovascular Responses from Skeletal Muscle Receptors 4.1 Effect of Activation of Afferent Fibers 4.2 Effect of Induced Muscular Contraction (Simulated Exercise) 5 Interaction of Muscle Afferents with Other Cardiovascular Reflexes 5.1 Arterial Baroreceptors 5.2 Cardiopulmonary Vagal Afferents 6 Role of Skeletal Muscle Afferents in Cardiovascular Response to Exercise in Humans 6.1 Dynamic and Static Exercise 6.2 Central Control (Central Command) 6.3 Peripheral Control 6.4 Integration of Neural Control Mechanisms During Exercise 7 Conclusion

Diagnostic relevance of humoral and cytotoxic immune reactions in primary and secondary dilated cardiomyopathy

Abstract: Circulating muscle-specific antimyolemmal antibodies (AMLAs) were found in 18 of 61 patients with secondary dilated cardiomyopathy (DC). All 18 patients had clinical or histologic evidence of previous perimyocarditis. AMLAs were found both in patients' serum samples and bound to the sarcolemmal sheath of the autologous myocardial biopsy specimen. Only AMLAs in postmyocardiac DC induced cytolysis of vital cardiocytes in the presence of complement, whereas hepatocytes remained unaffected. Titers of AMLAs correlated with the degree of cardiocytolysis. In contrast, antiinterfibrillary antibodies were found in 49 % patients with primary DC (n = 79) and in 61 % of patients (n = 30) with alcoholic DC. The incidence of antifibrillary antibodies of the antimyosin type was 23 and 24%, respectively. Incidence of both antibodies increased according to the severity assessed by New York Heart Association functional classes. Circulating immune complexes assayed by a new Clq-solid phase fluorometric assay were present in 30% of patients with postmyocarditic DC only. Lymphocyte-mediated cytotoxicity against heterologous cardiac target cells (K-cell activity) was measured in 33% of patients each with primary and secondary alcoholic DC but not postmyocarditic DC. There were no blocking factors in primary but were some in alcoholic heart disease.

Electron‐Rich Half‐Sandwich Complexes—Metal Bases par excellence

Abstract: Electron-rich, half-sandwich complexes of the type CnRnML2 or CnRnMLL′ are built up of an aromatic five- or six-membered ring, a d8-metal, and either a pair of two-electron donors or an equivalent chelating ligand. Such complexes behave like Lewis bases and react with a wide variety of electrophiles, El or ElX, to form products with a new metal-element bond. According to their reactivity they are comparable to the Vaska-type compounds. Certain of the products obtained after addition of the electrophile undergo interesting subsequent reactions in which, for example, metal complexes containing molecules that are unstable in the free state, such as CS, CSe, CH2S, CH2Se, CH2Te, CH3CHS, CH3CHSe, CH2CS, CH2CSe, and CH2CTe are formed. Moreover, cycloadditions as well as reactions with coordinatively unsaturated transition-metal compounds which result in formation of heterometal binuclear complexes demonstrate that the metal bases CnRnML2 and CnRnMLL′ are valuable synthetic building blocks. Furthermore, very recent investigations have indicated links between metal basicity and the problem of CH activation.

Chlorophyll fluorescence yield changes as a tool in plant physiology I. The measuring system

Abstract: A part of the light absorbed by green plants, is re-emitted in form of chlorophyll (Chl) fluorescence. This constitutes a large optical signal which can be easily detected, provided the wavelength of excitation is chosen so as not to overlap the wavelength of emission (670-770 nm). As early as 1874 N.J.C. MUller [1 ] observed Chi fluorescence changes in green leaves with his bare eyes, using a suitable combination of colored glasses. While already Mtiller [1] recognised a correlation between Chl fluorescence and assimilation, a systematic study of this correlation became possible only more than half a century later with the development of light sensitive devices and signal recorders, as first applied by H. Kautsky and his co-workers [2-5] Hence, progress in the study of Chl fluorescence has always been closely linked with advancements in measuring techniques. At present, such advancements are apparent e.g. in the fields of fiber optics, semiconductor photodevices, transient recorders and microcomputers. This article intends to give a brief survey of the different possibilities to measure Chl fluorescence changes. Emphasis will be put on such techniques which can be applied in plant physiological work. Forthcoming articles of this series will deal with the questions of how to interpret Chl fluorescence changes and how to apply this tool in the characterisation of the physiological state of the plant.

Properties of the Isolated Intact Chloroplast at Cytoplasmic K Concentrations : I. Light-Induced Cation Uptake into Intact Chloroplasts is Driven by an Electrical Potential Difference.

Abstract: Photosynthesis, stroma-pH, and internal K + and Cl − concentrations of isolated intact chloroplasts from Spinacia oleracea , as well as ion (K + , H + , Cl − ) movements across the envelope, were measured over a wide range of external KCl concentrations (1-100 millimolar). Isolated intact chloroplasts are a Donnan system which accumulates cations (K + or added Tetraphenylphosphonium + ) and excludes anions (Cl − ) at low ionic strength of the medium. The internally negative dark potential becomes still more negative in the light as estimated by Tetraphenylphosphonium + distribution. At 100 millimolar external KCl, potentials both in the light and in the dark and also the light-induced uptake of K + or Na + and the release of protons all become very small. Light-induced K + uptake is not abolished by valinomycin suggesting that the K + uptake is not primarily active. Intact chloroplasts contain higher K + concentrations (112-157 millimolar) than chloroplasts isolated in standard media. Photosynthetic activity of intact chloroplasts is higher at 100 millimolar external KCl than at 5 to 25 millimolar. The pH optimum of CO 2 fixation at high K + concentrations is broadened towards low pH values. This can be correlated with the observation that high external KCl concentrations at a constant pH of the suspending medium produce an increase of stroma-pH both in the light and in the dark. These results demonstrate a requirement of high external concentrations of monovalent cations for CO 2 fixation in intact chloroplasts.

The random elements in the systematic search behavior of the desert isopod Hemilepistus reaumuri

Abstract: Most of the year the isopod crustacean Hemilepistus reaumuri depends for survival on the protection of a permanent shelter (i.e., the burrow occupied by its family), despite its remarkable physiological adaptations to its desert habitat. If an isopod gets lost after an excursion from the burrow, it has to find it as quickly as possible. Displacement experiments show that H. reaumuri is indeed successful in homing. Even if a desert isopod is displaced in an arbitrary direction over a distance (starting distance r 0) from the burrow that exceeds 15 times the distance from which it can detect the entrance, it returns on average in less than 400 s. The homing behavior of H. reaumuri is successful not because of the isopod's ability to navigate to its burrow by using external orientation stimuli but because of the intrinsic structure of its search pattern. An isopod that is displaced from its burrow first searches approximately in the form of a spiral, then it moves through increasing loops on which meanders are superimposed. It concentrates these subunits of its search around the starting point by occasionally returning there. The time course of the azimuthal direction component of its position is not clearly regular. The surroundings of the starting point are searched evenly in every direction. The search behavior of H. reaumuri is composed of systematic subunits together with many random elements. The form of discrete brownian (random) search without directional correlations between its steps that best describes the observed behavior of H. reaumuri for search-path segments with a length between 1 and 7 m has an average step length of 33 cm. For segments with a searchpath length below 1 m the agreement between theory and observations is better if one starts from a discrete brownian search with a much smaller step length (one body length), but in which the direction of the steps is strongly correlated. Despite these geometrical similarities to a brownian search the search behavior of H. reaumuri is distinctly more successful because of the combination of two characteristics. H. reaumuri avoids the disadvantage of the most successful form of a brownian search (i.e., the frequent passage through a region in which it has searched just before) by moving in straighter lines. A brownian search with the same directional constancy shown by H. reaumuri would be inefficient because the thoroughness with which a given region is searched would be too low. H. reaumuri avoids this problem and concentrates its search around the starting point by sometimes returning to that place.

Interference between non-A, non-B and hepatitis B virus infection in chimpanzees.

Abstract: Pre-existing chronic or concurrent acute non-A, non-B (NANB) virus infection has been found to interfere with hepatitis B virus (HBV) replication and to delay and moderate markedly the appearance of disease related to HBV infection in chimpanzees. The mechanism for this phenomenon remains unclear. These findings are of practical significance for vaccine safety testing and evaluation of methods for virus inactivation in chimpanzees. The possible occurrence of dual NANB and HBV infection requires that prolonged follow-up be carried out. Attempts to carry out inactivation studies on materials containing both types of virus may also provide misleading observations.

The search behavior of the desert isopod Hemilepistus reaumuri as compared with a systematic search

Abstract: To protect itself from the extreme heat and dryness of its habitat in summer, Hemilepistus reaumuri must spend most of the time in its burrow. However, to forage it has often to make large excursions. As a rule it is able to return from any point to the entrance of the burrow by the shortest way. If a returning isopod misses the entrance by a few millimeters, it must search for it. Not until the second antennae have nearly touched the edge of the burrow entrance does an isopod detect it, by means of chemoreceptors in the terminal antennal segment. Even when the entrance is within reach of the antennae occasionally the animal will not detect it. H. reaumuri searches for the entrance of its burrow in a systematic and successful manner. If the excursion has covered only a short distance, it searches initially in a spiral pattern. If the burrow is not found during this phase the animal extends its range, moving in broad loops and meanders, but returns repeatedly to the starting point of the search. The problem H. reaumuri must solve in finding its burrow is described in quantitative terms. It is assumed that before the search begins the animal does not know the exact position of the entrance but possesses information about the probability density for this position. The difficulties encountered in detecting the burrow entrance are also taken into account. There is a very small probability that an isopod will detect the entrance if it searches only superficially in the region where the entrance actually is, but this probability increases rapidly with the intensity of search. For this reason it is advantageous for H. reaumuri to return after a while to a region it has already searched without success. The theoretical systematic form of search with the highest probability of success is derived under these conditions. The search behavior of H. reaumuri is as effective as this systematic form of search. The isopods also follow the most important rules governing the spatiotemporal properties of this pattern. They concentrate their search within a narrowly circumscribed region around the starting point. In all regions further away search would be unprofitable, for the increase in probability of success achieved by searching in these regions as well is too small in comparison with the additional search time required. Because this region continually expands as long as the search is unsuccessful, the isopods search over progressively larger areas until they have reached their goal.

Transport of hemolysin by Escherichia coli

Abstract: The hernolytic phenotype in Escherichia coli is determined by four genes. Two (hlyC and hlyA) determine the synthesis of a hemolytically active protein which is transported across the cytoplasrnic membrane. The other two genes (hlyB8 and hlyBb) encode two proteins which are located in the outer membrane and seem to form a specific transport system for hemolysin across the outer membrane. The primary product of gene hlyA is a protein (protein A) of 106,000 daltons which is nonhemolytic and which is not transported. No signal peptide can be recognized at its N-terrninus. In the presence of the hlyC gene product (protein C), the 106,000-dalton protein is processed to the major proteolytic product of 58,000 daltons, which is hemolytically active and is transported across the cytoplasmic membrane. Several other proteolytic fragments of the 106,000-dalton protein are also generated. During the transport of the 58,000-dalton fragment (and possible other proteolytic fragments of hlyA gene product), the C protein remains in the cytoplasrn. In the absence of hlyBa and hlyBb the entire hemolytic activity (mainly associated with the 58-,000-dalton protein) is located in· the periplasm: Studies on the location of hernolysin in hlyBa and hlyBb mutants suggest that the gene product of hlyB 8 (protein B 8 ) binds hemolysin and Ieads it through the outer membrane whereas the gene product of hlyBb (protein Bb) releases hemolysin from the outer rnembrane. This transport system is specific for E coli hemolysin. Other peri­ plasmic enzymes of E coli and heterologous hemolysin (cereolysin) are not transported.

Cardiac hypertrophy in rats after supravalvular aortic constriction. II. Inhibition of cellular autophagy in hypertrophying cardiomyocytes.

Abstract: Adult male Sprague-Dawley rats were killed by retrograde perfusion fixation 3, 7, 14, 21 and 35 days after supravalvular aortic constriction (n = 33) or sham-operation (n = 25). Subepicardial specimens of the left ventricular myocardium were evaluated by conventional electron microscopic morphometry, and in addition were examined for the occurrence of autophagic vacuoles (AVs) using large test areas (3.9 X 10(4) micron 2 per animal). The quotient of mitochondrial to myofibrillar volume fraction was largely unchanged during hypertrophy but was reduced by 25% compared with controls after termination of growth at 35 days. During the process of hypertrophy which eventually led to an increase in average single cell volume of the cardiomyocytes by 78%, the volume fraction and the numerical density of AVs was significantly lower than in sham-operated rats. The most striking difference was observed 7 days after the operations, the stage at which the growth rate of the cardiomyocytes relative to controls was at its maximum of 4.5% per day. At this point the volume fraction as well as the numerical density of AVs were reduced by about 50% compared with controls. At 14 and 21 days after operation, when the relative growth rate of the hypertrophying cardiomyocytes was still 2% and 1% per day, the AV volume fraction was reduced to a lesser extent (by 47% and 28%, respectively). After termination of adaptive growth at 35 days significant differences in fractional volume and numerical density of AVs were no longer detectable. These results suggest that degradation of cytoplasmic components is inhibited in cardiomyocytes undergoing hypertrophy. Such an anticatabolic reaction seems to play an important role in establishing the positive balance of cellular metabolism generally required for growth processes.

Defective translation of measles virus matrix protein in a subacute sclerosing panencephalitis cell line

Abstract: Subacute sclerosing panencephalitis (SSPE) is a slowly progressing fatal human disease of the central nervous system (CNS) that is associated with measles virus persistence. Virus nucleocapsids are present in the brain1,2 and the patient is in a state of hyperimmunization towards this agent. However, although all other structural polypeptides are recognized by the immune system, there is a markedly decreased antibody response towards virus matrix or membrane protein3,4. Matrix protein has not been detected in brain cells5 and infectious virus is not present. The absence of this virus structural polypeptide is thought to account for the apparent restriction in virus maturation both in vivo and in vitro. SSPE viruses can only rarely be rescued from brain tissue by co-cultivation or cell fusion techniques using tissue culture cell lines susceptible to measles virus infection6. Often this procedure fails to yield a lytic budding virus but produces instead a carrier cell line in which the agent is cell associated. These lines (known as SSPE cell lines) also do not contain matrix protein7,8. However, the reason for this deficiency is unknown. We have therefore now examined an SSPE cell line which does not yield infectious virus in order to define this process further. We found that although messenger RNA for membrane protein was present, it was unable to form normal matrix protein in translation reactions.

Progressive multifocal leucoencephalopathy: Detection of papovavirus jc in kidney tissue

Abstract: Cellular DNA of the kidney from a patient with PML was analyzed by reassociation kinetics for the presence of JC virus DNA. Various amounts of viral DNA sequences were detected in different areas of the kidney. The highest concentration (175 genome equivalents/cell) was found in the renal medulla and there were almost none in the renal cortex. Differentiation from the closely related BK virus was carried out by reassociation kinetics and restriction enzyme cleavage with subsequent Southern blot analysis. The enzyme Hind II, which does not cleave within the BK virus genome, generated four restriction enzyme fragments in the cellular DNA from the kidney, thus documenting the presence of JC virus DNA. By examination of the renal DNA with the "no-cut" restriction enzyme XHO I and the "one-cut" enzymes Eco RI and BAM HI it was possible to show that free and not integrated viral DNA was present in these cells. Nonhomogeneous defective DNA bands were not detectable. By in situ hybridization the epithelial cells lining the collecting tubules were found as predominant site of the viral infection in the kidney.

Flow cytometric analysis of factors which influence the BrdUrd-Hoechst quenching effect in cultivated human fibroblasts and lymphocytes.

Abstract: Human fibroblasts and lymphocytes were grown in bromodeoxyuridine (BrdUrd) containing medium, harvested after 27-71 hours and stained with the fluorochrome Hoechst 33258. Parameters that influence the BrdUrd quenching effect of Hoechst fluorescence at a given pH and ionic strength of the staining solution were determined. The parameters were determined in order to obtain high resolution histograms with differentiation of each cell cycle compartment for noncycling cells and for cycling cells in the first and second cycle. The BrdUrd concentration was found to be the most significant determinant, but cell density, cell type, dye concentration, type of Hoechst stain and incubation temperature during staining also contribute to the modulation of fluorescence of BrdUrd substituted nuclei. Optimization of these factors is required in order to achieve complete and well resolved cell cycle histograms by the BrdUrd-Hoechst flow cytometric technique.

Solution of Large Linear Systems of Equations by Conjugate Gradient Type Methods

Abstract: In 1952, Hestenes and Stiefel introduced the conjugate gradient algorithm in their landmark paper [27] as an algorithm for solving linear equation Ax = b with A as positive definite n × n-matrix (see the book [26] of Hestenes for a broad exposition) The algorithm fascinated numerical analysts since then for various reasons: The cg-algorithm combines features of direct and iterative methods which attracted the attention in the early years: It generates a sequence x i of vectors approximating the solution $$\overline x$$ in a defined way like other iterative methods, but like direct methods, terminating with the exact solution after at most n steps, at least in theory Many expectations were disappointed, when it was found out that due to roundoff the n-step termination property does not hold in practice However, viewed as an iterative method, the cg-algorithm has very attractive features Its application for the iterative solution of large sparse systems has been discussed very early [11] by Stiefel and his coworkers Like other iterative methods, it essentially requires only the formation of one matrix-vector product A·x per iteration, so that the iterations are inexpensive even for large matrices A, if they are sparse The iterative aspect of the method has been particularly emphasized since the work of Reid [38]

The role of accessory cells in polyclonal T cell activation. I. Both induction of interleukin 2 production and of interleukin 2 responsiveness by concanavalin A are accessory cell dependent

Abstract: Recent studies from other laboratories have shown that concanavalin A (Con A) acts at two separate steps in polyclonal T cell activation: interleukin 2 (IL2) production, and induction of responsiveness to IL2. Using a combination of techniques for the depletion of accessory cells from lymph node T cells, we have investigated which of these steps, if not both, is responsible for the known requirement for accessory cells in the Con A response. It was found that with increasing T cell purification, first the ability is lost to produce sufficient levels of endogenous IL2, whereas induction of IL2 responsiveness can still take place. Further removal of accessory cells however yields a population of resting T cells that cannot be induced by Con A to become IL2-reactive. It was concluded that both IL2 production and induction of reactivity to IL 2 are accessory cell-dependent events.

Occurrence of an Inhibitory Guanine Nucleotide‐Binding Regulatory Component of the Adenylate Cyclase System in cyc− Variants of S49 Lymphoma Cells

Abstract: In membranes of S49 lymphoma cyc− variants, which lack a functional guanine nucleotide-binding component (Ns protein) mediating adenylate cyclase stimulation by hormones, guanine nucleotides decreased the forskolin-stimulated adenylate cyclase activity by maximally 40–60% The potency order of the guanine nucleotides studied was guanosine 5′-[γ-thio]triphosphate(GTP[S])> guanosine 5′[β,γ-imido]triphosphate ≫ GTP > guanosine 5′-[β-thio]diphosphate (GDP[S]) GTP and GDP[S] acted as partial inhibitors; they competitively antagonized the GTP[S]-induced inhibition, which was half-maximal and maximal at about 3 nM and 100 nM GTP[S], respectively Cholera toxin did not enhance the inhibitory action of GTP The cyc− adenylate cyclase inhibition by GTP[S] occurred after a short lag period and persisted after washing the membranes The inhibition was not affected by the pH (65–90) of the incubation medium and was largely independent of the concentrations of MgATP (up to 200 μM) and Mg2+ (up to 10 mM) In contrast, Mn2+ potently reduced the GTP[S]-induced cyc− adenylate cyclase inhibition Similarly as observed with forskolin, GTP[S] decreased the cyc− adenylate cyclase activity stimulated by purified, preactivated Ns protein Apart from Mn2+, inhibition of the cyc− adenylate cyclase by GTP[S] was prevented or reversed by various treatments, which have been shown to obliterate hormone-induced adenylate cyclase inhibition in other cell types, such as by N-ethylmaleimide, by limited proteolysis with trypsin and by a factor extracted from bovine sperm particles The data indicate that in membranes of cyc− variants, which lack a functional Ns protein, a guanine nucleotide-binding component (Ni) is present, which mediates adenylate cyclase inhibition by guanine nucleotides Such a component apparently also mediates adenylate cyclase inhibition by hormones in other cell types Comparison of adenylate cyclase stimulation and inhibition by guanine nucleotides suggests that Ni is activated and inactivated by similar but not identical mechanisms as the Ns protein and that the relative activity states of these coupling components determine the activity of the adenylate cyclase

Personality traits versus the quality of the marital relationship as the determinant of marital sexuality.

Abstract: The question of whether personality traits or the relationship among marital partners is more significant for the importance of sexuality and satisfaction in sexual interaction was examined. It was demonstrated that only interaction variables were significant, satisfying sexual relationships existing only in happy marriages. Correspondence between the partners was quite good for “satisfaction in sexual interaction,” but there was no correlation for the importance sexuality had for both partners. The comparison between the two sexes additionally showed that for women sexuality was less important and satisfying compared to men. This relationship held during various stages of the marital relationship.

The isotope effect of tritium in3H-noradrenaline

Abstract: In a variety of tissues of organs3H-(−)-7-,3H-(−)-7,8 and3H-(−)-2,5,6-noradrenaline were compared, partly also with unlabelled (−)-noradrenaline. The following isotope effects were found: 1. Neuronal uptake (vas deferens, rabbit heart): tritium reduced the neuronal uptake by a factor of 1.3 to 2.0 (reduction:3H-7-<3H-7,8-<3H-2,5,6-noradrenaline). 2. Extraneuronal uptake (rat heart): tritium reduced the extraneuronal uptake of noradrenaline by a factor of 1.3 to 1.8 (reduction:3H-7-<3H-7,8-<3H-2,5,6-noradrenaline). 3. Monoamine oxidase (MAO; homogenates of rat heart):3H-7-noradrenaline was a better substrate than was unlabelled noradrenaline, but3H-7,8- and3H-2,5,6-noradrenaline were inferior substrates. 4. Neuronal and extraneuronal deaminating systems: in the intact cells of the rat vas deferens (neuronal deaminating system) or of the rat heart exposed to cocaine (extraneuronal deaminating system) the low rate constant characterizing the deamination of3H-7,8- and3H-2,5,6-noradrenaline resulted in high intracellular concentrations of3H-noradrenaline; consequently, the low rate constant failed to greatly affect steady-state rates of deamination. 5. Catechol-O-methyl transferase (COMT): in rat heart homogenates the rate constant for the O-methylation of3H-noradrenaline was: unlabelled (−)-noradrenaline=3H-(−)-7-noradrenaline>3H-(−)-2,5,6-noradrenaline. 6. Extraneuronal O-methylating system (rat heart exposed to cocaine): steady-state rates of formation of3H-NMN were higher for3H-7- than for3H-7,8-noradrenaline, but an inverse relationship was found for the intracellular accumulation of labelled amine.

Exchange-Split Empty Energy Bands of Fe(110)

Abstract: Spin- and momentum-resolved bremsstrahlung isochromat spectra from Fe(110) at $\ensuremath{\hbar}\ensuremath{\omega}=9.7$ eV are presented, a combination which allows for the first time the determination of experimental final-state dispersions $E({k}_{\ensuremath{\parallel}})$ for direct interband transitions into majority and minority final bands separately. Data are in good agreement with relevant theoretical $E({k}_{\ensuremath{\parallel}})$ values from bulk band-structure calculations as far as minority final states are concerned. Theoretical predictions for the majority states exhibit a stronger dispersion than observed experimentally.

Formation of stable preinitiation complexes is a prerequisite for ribosomal DNA transcription in vitro

Abstract: Cytoplasmic extracts from cultured mouse cells contain the factor(s) required for specific transcription initiation of rDNA by RNA polymerase I. Prior to transcription the essential proteins bind to the ribosomal gene and remain bound to the template for several rounds of transcription. The assembly of these preinitiation complexes in vitro has been demonstrated by kinetic analysis of the transcription reaction and by competition experiments. Complex formation involves an initial, rapid binding of transcription factor(s) to rDNA sequences followed by additional events which arrange the DNA-protein complex into a transcriptionally active state. Once the complexes have formed they persist for at least 2 hours in vitro and are resistant to elevated salt concentrations. The assembly of the complexes was inhibited when the template DNA was incubated with histones prior to the addition of S-100 extract. If, however, preinitiation complex formation was allowed to occur before the addition of histones, the interference of histones with specific transcription was much less pronounced.

Corticotropin peptides and melanotropins elevate the level of adenosine 3':5'-cyclic monophosphate in cultured murine brain cells.

Abstract: Cell cultures derived from mouse and rat brain and consisting mainly of astroblasts are known to respond to several hormones by increasing or decreasing their intracellular concentration of cyclic AMP. In the present study these cultures were analyzed for their susceptibility to various additional hormonal and other neuroactive compounds. Only the peptides of the corticotropin (ACTH)/melanotropin (MSH) family were found active. Their potency for elevating the intracellular level of cyclic AMP decreases in the sequence (values for the half-maximally stimulating concentrations, EC50, in parentheses) ACTH-(1-24) (10 m) greater than alpha-,beta-MSH (30 nm) greater than ACTH (greater than or equal to 100 nm) gamma-MSH, ACTH-(1-10), -(4-10), -(4-11) (greater than or equal to 0.5 microM). The lack of additivity of the maximal effects of the peptides suggests that they all act at the same receptor. The stimulation exerted by these peptides is partially suppressed by hormones known to inhibit cyclic AMP formation in that culture, i.e., noradrenaline (acting via an alpha-adrenergic receptor), adenosine (acting via an A1 receptor), and somatostatin. It is concluded that the receptors for the ACTH/MSH peptides and the inhibitory hormones are located on the same cells, presumably the astroblasts. The maximal response to ACTH and alpha- and beta-MSH depends strongly on the age of culture. The results are discussed in view of the facts that (1) peptides of the ACTH/MSH family affect behavior and learning in animals, and (2) ACTH and alpha-MSH occur in brain.