Voprosy biokhimii mozga最新文献

The identity of one of the acid neurospecific antigens (antigen A) and S-100 protein has been established through agar gel immunoelectrophoresis and Sephadex G-100 gelchromatography. On agar gel electrophoresis antigen A moves as 2 fractions which occupy positions of blood serum prealbumins and alpha2 globulins. Both fractions of the antigen have a molecular weight of 25000. The heterogenic nature of antigen A (protein S-100) during electrophoresis on agar gel is discussed.

Our studies have shown that malatedehydrogenase of rat brain mitochondrial fraction (M-MDH) and soluble fraction (S-MDH) differ in respect to their coenzyme specificity. Affinity of both M-MDH and S-MDH to deamino-NAD (direct reaction) is about two times lower than toward NAD. In the reverse reaction deamino-NADH and NADH enhance the activity of M-MDH to the same extent while in the presence of deamino-NADH the activity of S-MDH is somewhat higher. The isoenzyme composition of M-MDH and S-MDH have been studied as well as the relative affinity of each isoenzyme towards deamino-NAD and NAD. Both M-MDH and S-MDH have been shown to consist of 3 isoenzymes, the second isoenzyme being the most active. The percentage of the 3-rd isoenzyme is the lowest. The coenzyme affinity of isoenzymes M-MDH and S-MDH have been shown to differ very markedly.

The investigations carried out have shown that not only AMP but ADP also undergoes direct deamination in both soluble and mitochondrial fractions of rat brain tissue. Deamination of AMP is stimulated by the addition of ATP and the activity of one of the isoenzymes of AMP-aminohydrolase is markedly enhanced by both yeast and brain hexokinase. Activation by hexokinase is mainly due to its SH groups, through which hexokinase reacts with AMP-aminohydrolase, forming, probably, a protein-protein complex in which AMP aminohydrolase activity is considerably increased. Hexokinase does not affect the deamination of ADP and NAD. Further experiments are needed to find out whether the activation of AMP-aminohydrolase is accomplished by hexokinase itself or by an other protein contaminating it. Deamination of NAD, in contrast to AMP and ADP, takes place only in mitochondria and does not occur in the soluble fraction. In mitochondria besides deamination, AMP and ADP undergo intensive dephosphorylation, while the deamination of NAD is not accompanied by an increase of phosphate, i. e. mitochondria lack enzymes which breakdown NAD to mono nucleotides. Our data indicate that the formation of deamino -NAD from NAD and reamination of deamino-NAD by aspartate to NAD by the formation of intermediary NAD-succinate is of greater importance. The formation of the latter and that of deamino-NAD from NAD as well as the presence of preformed deamino-NAD in mitochondria have been demonstrated by Movsessian. The occurrence of these processes in mitochondria and their role in the formation of ammonia from amino acids is of importance in as much as oxaloacetate formation and its conversion to aspartate, which is necessary for the reamination of deamino-NAD, are localized in mitochondria. The main source of the amino nitrogen of aspartate is known to be glutamate, which incorporates the amino nitrogen of most amino acids. alpha-Keto-glutarate, which is necessary for the synthesis of glutamate, is also formed in mitochondria are the most favourable site for the formation of ammonia from amino acids with the participation of pyridine nucleotides. Of the purine mono and dinucleotides studied deamino-NAD is most effective in the formation of ammonia from amino acids in mitochondria since in contrast to purine mono nucleotides, deamino-NAD and NAD are not dephosphorylated in mitochondria. According to some authors the reamination of IMP by aspartate is of importance in the formation of ammonia from amino acids in brain tissue. In our studies, however, IMP was not effective in the formation of ammonia from aspartate in mitochondrial fractions. IDP was found to be more effective. IMP and IDP may probably participate in the formation of ammonia in the soluble fraction, where nucleotidase activity is considerably low.

Some properties and phospholipid composition of proteolipids (PL) of brain of 10, 20, 30 and 120--180 days old rats were studied following their isolation by the emulsion centrifugation method of Folch. The content of crude and purified PL and the phospholipids bound to them gradually increased with age. The PL isolated from brains of 10-day old rats are different in their properties and composition from that of PL of adult brain. Their optical density is 2-2,5 times smaller (E1% 1cm lambda 278 mmk). This may be due to their lower content of cyclic amino acids. The content of lecithin and monophosphoinositides in PL decreases with age while that of serienphosphatides and especially polyglycerophosphatides increases. The content of acidic phosphatides tightly bound to PL protein also increases. All of these changes occur mainly between the 10th and 20th days after birth. It would seem that this period is important for the formation of PL and their involvement in the composition of membranes.

The content and hydrophobic properties (distribution coefficient in hexan : water) of organophosphorus inhibitors OPT of the following structure--R-O (CH3)/P/O/S C2H4SC2H5 have been studied in rat brain. On enlargement of the O-alkyl radical from ethyl to isopropyl and pinacolin hydrophobecity increases from 1 to 12 and 39, while the relative content of the chloroform extractable free OPT in brain, under conditions of uniform distribution, decreases from 11--18% to 3.2%. On incubation of the homogenate at 37 degrees C the further inhibition of the specific cholinesterase of the brain indicates the presence of an absolutely free form of OPT, the amount of which is not dependent on the degree of its hydrophobicity.

In rats learning to use nonpreferred paw is accompanied by an increase of acetylcholinesterase (AChE) of specific areas of rat cerebral cortex and pyramidal neurones of CA3 and CA4 of the hippocampus. Following achievement of new behavioural reactions high AChE activity is preserved longer in the neacortex, the enzyme activity in the pyramidal neurones of the hippocampal cortex coming to normal. Following preliminary intracranial administration of puromycin the increase of AChE activity during learning is no more observed. This indicates the activation of the genetic apparatus during learning and training as a result of which synthesis of membrane proteins including AChE is enhanced. A close correlation between learning and the inductive synthesis of AChE is observed. Lateralization of the chemical traces of learning in specific areas of rat cerebral cortex are observed as increased activity of AChE. Changes in AChE activity in various hemispheres of rat brain during learning are thought to be due to assymetric changes in the excitatory level of cortical sites during the formation of new behavioural reactions. The specific localization of biochemical changes in the brain is certainly more favorable from an energetic aspect and may by regarded as an evolutionary compensatory process. The interrelationship of the activation of the synthetic apparatus of the cell with the reception of external informations is one of the expressions of adaptation during codations of functions of the organism more advantageous from an evolutionary point of view.

Inasmuch as the highest concentrations of transmitter substances occur in the mesodiencephalic region of the brain, which according to our results possesses quite high Na+,K+-ATP-ase activity, in the present study we tried the effect of norepinephrine (NE) and gamma-aminobutyric acid (GABA) on Na+, K+-ATP-ase activity of rat mesodiencephalic region. The results obtained indicate that in homogenates NE (5-10(-4) M) stimulates Na+, K+-ATP-ase activity about 3.6 times, while equimolar amounts of GABA have no effect. Higher concentrations of GABA (1.10(-3) M and 3.10(-3) M), as well as changes in the length of the preincubation period with GABA, failed to affect enzyme activity. Effect of transmitters was next studied on ATP-ase activity of synaptosomal fractions of the mesodiencephalic region. Here also a statistically significant increase of enzyme activity was observed from NE but not from GABA. Changes in ATP-ase activity of rat brain synaptosomal fractions were also not observed in in vivo studies 20 min after i.p. administrations of 5 mg/kg GABA. The results of the present study indicate that NE stimulates Na+, K+-ATP-ase activity of rat brain mesodiencephalic region while under the given experimental conditions GABA does not seem to have any effect.

Quantitative changes of various forms of ribonucleic acids [nuclear (n-RNA), ribosomal (r-RNA), transport (t-RNA)] as well as ribonuclease activity have been studied in rat brain, in its nuclear, ribosomal and supernatant fractions following 3,5-cyclic AMP (c-AMP) and S-adenosyl-L-methionine. These substances were shown to raise the levels of r-RNA in brain and reduce the amount of n-RNA of GC type. c-AMP was also found to reduce the n-RNA of AU type and t-RNA in brain, while S-adenosyl-L-methionine does not affect n-RNA of AU type and raises considerably t-RNA. S-adenosyl-L-methionine has been found to raise the levels of all kinds of RNA while c-AMP has no effect. Ribonuclease activity of nuclear, ribosomal and supernatant fractions (105,000 g) of brain has been found to be enhanced by c-AMP while S-adenosyl-L-methionine raises ribonuclease activity of ribosomal fraction only at pH 7.9. The data obtained indicate that c-AMP and S-adenosyl-L-methionine are of importance in the mechanisms regulating the level of nucleic acids and activity of enzymes involved in their metabolism.

The quantitative isolation of loosely and tightly bound gangliosides of human brain has been studied following various ways of extraction. Hot methanol extraction (Bogoch's method) gave a higher level of tightly bound gangliosides than by extraction with the Folch method. Both kinds of gangliosides were found to have the same fractional composition on thin layer chromatography on silicagel. A single extraction method of gangliosides giving high yields is proposed.