Changes in H1 complement in differentiating rat-brain cortical neurons

Neuronal nuclei have a low H1 content. A stoichiometry of 0.47 molecule/nucleosome, on average, is calculated for rat brain cortical neurons by comparing its H1 content with that of liver nuclei. The H1 fraction of rat cerebral cortex neurons has been resolved into five subtypes, H1a--e, that have the same mobility as the unphosphorylated H1 forms of other rat tissues. The subtypes H1a--d decay exponentially during postnatal development and are substituted to different extents by H1e. The higher replacement rate is shown by H1a with an apparent half-lifetime of about 5 days. The corresponding values for H1b, H1c and H1d are 11, 21 and 15 days. Several conclusions can be drawn from the observation of postnatal changes in H1 subtype proportions. The low H1 content of neuronal nuclei does not imply the presence of notable peculiarities in subtype composition or in subtype substitution pattern. There is turnover of H1 in differentiating neurons once cell proliferation and DNA replication have ceased. The relative rates of synthesis and/or degradation of the subtypes differ in germinal cells and in neurons. Comparison with previous results on H1 degrees accumulation also shows that in cortical neurons the regulation of the subtypes H1a--e differs from that of H1 degrees.     

2,3-Bisphosphoglycerate protects mitochondrial and cytosolic proteins from proteolytic inactivation

2,3-bisphosphoglycerate at physiological concentration similar to that found in many tissues protects effectively ornithine transcarbamoylase (OTC) from proteolytic inactivation by broken lysosomes. 2,3-bisphosphoglycerate protects also many other mitochondrial and cytosolic proteins, such as glutamate dehydrogenase (GDH) an glyceraldehyde-3-phosphate dehydrogenase (GAPDH), from proteolysis by broken lysosomes and other proteases. It is, thus, suggested that 2,3-bisphosphoglycerate may play an important role in the control of the degradative rates of some proteins, which may explain its high concentration in certain cells.     

Protein and lipid disturbances in rat liver microsomal membranes after bile duct ligation

An analysis of proteins, phospholipids and cholesterol from liver microsomal membranes was performed in normal and post-cholestatic rats. Bile duct ligated rats showed a progressive decrease of these membrane constituents. Minor changes in peptide analysis, a marked decrease of phosphatidylcholine and phosphatidylinositol, disappearance of phosphatidylethanolamine and sphingomyelin, and a clear increment of phosphatidylserine was observed in post-cholestatic as compared to normal group. It was concluded that extra-hepatic cholestasis produces structural changes on the liver microsomes, particularly on phospholipid profile.     

Apocytochrome-c competes with pre-ornithine carbamoyl transferase for transport into mitochondria

Apocytochrome c, the cytosolic precursor of cytochrome c, competes with the precursor of ornithine carbamoyltransferase (OCT) for entry into isolated rat liver mitochondria.     

Limited proteolysis reveals low-affinity binding of N-acetyl-L-glutamate to rat-liver carbamoyl-phosphate synthetase (ammonia)

Carbamoyl-phosphate synthetase was inactivated by elastase with first-order kinetics, and N-acetyl-L-glutamate speeded inactivation. From the dependence of the t1/2 value for inactivation on the concentration of acetylglutamate we estimate a Kd value for binding of the activator of 0.365 mM, which is approximately 600 times greater than in the presence of ATP, HCO3-, K+ and Mg2+. K+ and Mg2+ are not required for binding with low affinity, and in the absence of ATP they do not appear to increase the affinity for acetylglutamate. In the presence of acetylglutamate, mixtures of ATP, K+ and Mg2+ protect the enzyme from inactivation. ADP or AdoPP[NH]P partly replaced ATP in protecting the enzyme and thus binding of the nucleotide without further reaction is enough for protection. Two partial activities of the enzyme were inactivated by elastase to the same extent as the overall reaction, and thus elastase affects some property of the enzyme which is essential for catalysis. With other proteinases tested, inactivation was also accelerated by acetylglutamate and was slowed by mixtures of ATP, K+, Mg2+ and acetylglutamate, suggesting that changes in the accessibility of susceptible bonds are responsible for the changes in the degree of inactivation. It is concluded that elastase attacks at or close to the binding sites for ATP, and that exposure of the binding site for the ATP molecule that yields Pi (ATPA) upon binding of acetylglutamate causes the acceleration of the proteolytic inactivation.     

G2 effects of DNA-repair inhibitors on chromatid-type aberrations in root-tip cells treated with maleic hydrazide and mitomycin C

In recent years the existence of a DNA-repair process in G2 has been proposed to explain the potentiating effects of DNA-repair inhibitors given in G2 on chromatid aberrations (CA) induced by S-dependent as well as S-independent DNA-damaging agents. In the present report, root-tip cells of Allium cepa were exposed to maleic hydrazide (MH) or mitomycin C (MMC) and post-treated in G2 with caffeine (Caff) and various inhibitors of DNA synthesis. No enhancement of chromosome damage was observed when Caff was present in G2, but hydroxyurea (HU) or 5-fluorodeoxyuridine (FdUrd) potentiated the frequencies of CA. A slight additional increase of CA frequencies was observed following treatment with Ara C and excess thymidine in G2. When MH-damaged cells were pulse-treated with Caff earlier during recovery, the yield of CA was enhanced. The earlier Caff was present following MH treatment, the stronger was the potentiation.     

Various parameters of humoral and cellular immunity in children with iron deficiency

Serum IgA, IgM and IgG as well as percentage of lymphocytes T and B in peripheral blood were determined in 50 children aged between 6 months and 3 years with iron deficiency anaemia. A significant decrease in lymphocyte T number in these children was found in comparison with control group of healthy children. Lymphocyte T count positively correlated with serum iron concentration. Moreover, a decrease in serum IgA and IgG was found in children with iron deficit.     

The effect of glucose and ammonium sulfate on kinetic acidification by heterogeneous mixed culture

Summary The effect of glucose and ammonium sulfate concentration on the kinetics of lactic acid formation by a heterogeneous mixed culture was evaluated by the sole product formation using the Gompertz model, which can be used to define culture media composition taking into account product accumulation and acidification rate constant. A compromise between ionic inhibition and nitrogen limitation was found by using ammonium sulfate as nitrogen source. The sugar tolerance was similar to that in exenic cultures.     

Utilization of alanine for glucose formation in isolated rabbit kidney-cortex tubules

In kidney cortex tubules isolated from fed rabbits L-alanine is not utilized as glucose precursor, when added as a sole substrate. However, this amino acid decreases gluconeogenesis from low (up to 1 mM) 2-oxoglutarate concentrations and stimulates this process at higher (2.5-10 mM) ketoacid contents in the suspension medium. Aminooxyacetate, an inhibitor of aminotransferases, abolishes both inhibitory and stimulatory effects of L-alanine on glucose formation. The addition of 2-oxoglutarate increases the incorporation of L-[U-14C]alanine to glucose from 8- to 123-fold, depending upon the ketoacid and alanine concentrations used. In contrast, nonlabelled L-alanine decreases the incorporation of low [U-14C)2-oxoglutarate concentrations into glucose, while it does not affect contribution of 5 mM ketoacid to gluconeogenesis. The data indicate that (i) in the presence of 2-oxoglutarate L-alanine is utilized as glucose precursor in rabbit renal tubules and (ii) this amino acid may decrease the contribution of low extracellular concentrations of the ketoacid to gluconeogenesis.