Biomedical subjects
Publications and source records attributed to A D Braun.
New data are presented on ADP-ribosylation of nuclear proteins, which is one of the paths of their postsynthetic modifications. The importance of this reaction for DNA cell cycle regulation are discussed. The structure of mono- and poly(ADPRib), the properties of their synthesis and degradation catalyzing enzymes, and the nature of the modified proteins are considered.
NADP-glycohydrolase and NADP-pyrophosphates activities were examined during the rabbit erythroid cell differentiation. The former is high in erythroblast lysates, especially in the erythroblast nuclei. As erythroid cell maturation proceeds, the activity of NADP-glycohydrolase decreases. At the first step (erythroblast-reticulocyte transformation), this activity falls down more than by 20 times, whereas at the second step (reticulocyte-erythrocyte transformation) it decreases no more than twice. NADP-glycohydrolase is associated with the stroma of erythroid cells throughout their maturation, being bound with the nucleus in erythroblasts. NADP-pyrophosphatase activity has been detected in reticulocytes and mature cells only. The role of NADP- and NAD-glycohydrolases for characterization of the intracellular metabolic pools is discussed.
Anoxia (during 2 minutes after decapitation) produced a significant elevation of cAMP contents (up to 410%) in mouse brain cells. This effect was abolished by an intraperitoneal injection of alloxan (A), morphine (M), and ethanol (E) 30 minutes before decapitation, and after a 2 minutes diethyl ether (DE) inhalation. It was found that anoxia produced some decrease in phosphodiesterase (FDE) activity. A preliminary injection of A and E produced an activation of FDE; M and DE did not change FDE significantly. Mechanisms of action of all the four agents on the cAMP content under anoxia are different. A and E produced a rapid cAMP hydrolysis on stimulating the activity of FDE, M and DE inhibited apparently adenylate cyclase. The activation of adenylate cyclase due to anoxia is considered as one of the initial steps in the cell injury extention.
Using phase-contrast and polarized ultraviolet (UV) fluorescent microscopy, the structure of single muscle fibres was studied in the course of the contraction module formation during Zenker's necrosis. The degree of manifestation of destructive changes in the contractile system was shown to depend upon the concentration of extracellular Ca-ions. With decreasing Ca2+ concentration, the fibre loses the ability to form contraction nodules peculiar to the Zenker necrosis, and the development of this process is interrupted at the stage of sarcomere supercontraction. The UV fluorescent anisotropy pattern of fibre regions, conforming with the contraction nodules, suggests the occurrence of a more pronounced disorganization of contractile system in the presence of Ca2+. The ATPase activity of actomyosin isolated from altered muscle was studied to appreciate the functional state of the contractile system. This actomyosin was found to be inactivated 1.5 times as much as that isolated from muscles treated during Zenker's necrosis in calcium-free media.
Changes in the extractability, and in the activity and ratios of active and inactive forms of phosphorylase (PhL) were studied under the action of heating and of urea on skeletal muscles of Rana temporaria L., and under the electric stimulation of the muscle. Besides, the action of these factors on the isolated enzyme was studied. Under the alteration of muscles due to heating, a decrease in extractability and in the activity of the whole PhL takes place. The isolated PhL is more thermostable than that in the intact muscle. Under the action of urea, a decrease in extractability and activity of the whole Phl occurs only with doses of urea which cause the irreversible alteration of muscle. In respect to urea stability, PhL in isolated state is one of the most labile enzymes of the water-soluble fraction. Under contractures produced by the action of heating and of urea, no transformation of an inactive PhL (PhL b) into the active PhL (PhL a) was revealed in the muscle. Under the tetanic contraction produced by the electric stimulation of muscle, a 2.5--3.0-fold increase of PhL a activity takes place under the invariable level of the whole PhL activity.
The effect of diphteria toxin on the synthesis and degradation of NAD+ and the hydrolysis of NADP+ in the nuclei of guinea pig kidney were studied. Treatment of animals with diphteria toxin (DT) results in considerable reduction of NADpyrophosphorylase activity, which starts 12 hours after incubation and is minimal (50% of that of the control animals) 18 hours after it. During this time interval DT does not affect the activity of NADase and decreases that of NADPase in the nuclei. Thus under diphterial intoxication a decrease of NADPase activity, the synthesis of NAD+ being reduced, probably provides for kidney cells more favourable conditions for maintenance of their synthetic reactions and for restoration of their normal metabolism. It was found that the non-ionic detergent Triton X-100 promotes the NADpyrophosphorylase activity in cell nuclei of intact animals by 40% (on the average) and does not affect the NAD+ synthesis in DT injected animals. Therefore DT not only reduces the nuclear NADpyrophosphorylase activity but also affects the nuclear envelope. The alteration of nuclei under DT treatment is suggested by the decrease of their histone content (30% on the average as compared with the control). The decrease of NADpyrophosphorylase activity under DT intoxication can be considered as an adaptive reaction limiting the availability of NAD+ as the substrate of the EF2 mono (ADP-ribosilation) which results in its unability to promote translation.
A study was made of the hydrolysis of NAD+ in the process of rabbit erythroid cell differentiation. Activities of NAD-hydrolase and NAD-pyrophosphatase, examined during maturation of erythroid cells, demonstrated a more significant decrease in the course of erythroblast-reticulocyte transformation, than at the next step of erythropoesis (reticulocyte-erythrocyte transformation). Both enzymes are strongly associated with the stroma. Under discussion is a question of the possible role of NAD+ catabolism.
A study has been made on changes of outflux, extractability and activity of phosphofructokinase (PPK) under the action of heating, and of urea on the frog's skeletal muscles and on their extracts. Under the action of heating on muscles, the decrease of PPK activity (to 35%) is first revealed 34--36 degress C, when decrease of excitability and the contracture are not yet detected, and the extractability of the total water-soluble protein does not change. At the start of contracture, and at the decrease of excitability (at 38 degrees C) PPK in the muscle loses its activity. The thermolability of PPK is the greatest one compared to all the enzymes investigated before. The data on the high thermolability of PPK are discussed in terms of the regulating role of PPK in glycolysis. The PPK activity of extracts of muscles altered by urea, during the action not accompanied by the death of muscles, does not change. At the irreversible disappearance of muscle excitability, PPK is inactivated. PPK in the cell is more stable to injuring agents than PPK in isolated state.
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The release and extraction of histones from the nuclei of guinea pig liver under the influence of diphteria toxin was investigated in vivo and in vitro. A considerable loss of nuclear histones, increase of easily extracted arginine-rich histones and a more complete extraction of lysine-rich ones have been shown. A possible role of histones in the development of diphteria intoxication is discussed.
Changes of protein composition within necrotic areas of muscle at the late stages of Zenker's necrosis (3--5 hours after damage) have been studied using the disc-DSN-electrophoresis method. These changes are presumably associated with a disarrangement of the structure of thick and thin fillaments. The disturbance of the contractile system is accompanied by the loss of water soluble protein specific fractions.
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The nature of a before unknown biological activity of NAD as a substrate in protein modification reaction is considered. Upon enzymatic digestion of NAD its adenosinediphosphate ribose (ADPR) part is transferred to acceptor proteins. ADPR in its mono- or polymeric form is covalently linked to proteins at the expense of NAD's high energy bound. Negatively charged ADPR, in association with a protein, is able to alter the charge, conformation and biological activity of the latter. The reaction is important in structural rearrangements of chromatin, in the synthesis and repair of DNA, in cell growth and differentiation and in the mechanisms of actions of actions of bacterial toxins.
Changes of outflux, extractability and activity of lactate dehydrogenase (LDG) and glucose-6-phosphate dehydrogenase (G-6PhDG) of muscles under the action of heating (at 32--44 degrees for 15 min) and urea (1 M during 10 min, 30 min, 2 hr. and 9 hr.) on the skeletal muscles of R. temporaria L. were studied. Under the thermal action not accompanied by contracture and fall of the excitability (32--36 degrees), the increase of outflux of LDG out of muscles into surrounding solutions is observed. G-6-PhDG in the external medium under any heating action was not revealed. Extractibility of LDG and G-6-PhDG did not change. Under the thermal action accompanied by the fall of excitability and by the contracture, along with the prolong increase of outflux of LDG, a decrease of extractability of LDG takes place. The decrease of G-6-PhDG is set at 42 degrees. Under the alteration of muscles by urea in the period of the temporary fall of excitability and contracture (10 and 30 min) an increase of the outflux of LDG out of muscles is observed. G-6PhDG in the surrounding medium was not revealed up to 9 hr. of incubation of muscle. In the period of the recovery of the excitability and relaxation of muscles (2hr.) the outflux of LDG approaches the control level. During the temporary loss and recovery of excitability, the extractability of LDG and G-6-PhDG does not change. In the period of irreversible contracture and loss of the excitability (6--10 hr.) a sharp increase of outflux of LDG out of muscles takes place. The extractability of the examined enzymes, especially of LDG, decreases.
CAMP in the wide range of concentrations (3.10(-7)--10(-3) M), cGMP (10(-6)--10(-5) M) and dibutyril-cAMP (3.10(-6) M) produced no effect on oxidative phosphorylation of rat liver mitochondria. Among histone fractions (H1, H3 and H4) tested, the arginine-rich fraction H3 (18 microgram/mg of mitochondrial protein) produced a strong uncoupling effect. It is supposed that the effect of cAMP on oxidative phosphorylation of mitochondria may be carried out indirectly through activation of protein kinase, phosphorylation of histones, and their release into the cytoplasm.
A study was made of changes in outflux, extractability and enzyme (aldolase and creatine kinase) activity of muscle proteins induced by thermal action in skeletal muscles of R. temporaria L. Under a 15-minutes action of temperatures under 36 degrees C, which do not produce any contracture or fall of excitability, changes in a fraction of protein outfluxed from muscles were observed. The thermal action accompanied by the fall and irreversible loss of excitability (above 36 degrees) resulted in the fall of extractability and enzyme activity of water-soluble proteins extracted from homogenized muscles in addition to prolonged changes in the fraction of outfluxed proteins. The increased binding of aldolase by actomyosin under thermal injury of muscle is established. Changes of outflux extractability and enzyme activity of proteins during the thermal alteration of muscle are considered with regard to data about the complexing of muscle proteins.
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