[The role of conformational changes in the functioning of brain Na,K-ATPase]. / O roli konformatsionnykh izmenenii v funktsionirovanii Na,K-ATFazy mozga.

In the experiments with enzyme preparations of Na,K-ATPase from normal brain tissue (NBT) and tumorous brain tissue (TBT) the following data were established: 1) the cooperativity of Na,K-ATPase with Na+ from NBT is temperature-dependent, the Hill coefficient (nH) at 37, 27.0-30.5 and 20-22 degrees C being 1.80 +/- 0.07, 1.30 +/- 0.09 and 1.10 +/- 0.08, respectively; the cooperativity of Na+ with Na,K-ATPase from TBT was absent; 2) the cooperativity for ouabain (nH-1.30 +/- 0.05) was revealed only in the case of Na-pump from TBT; 3) the protective effect of ATP against the inhibitory action of pCMB is temperature-dependent and differs significantly in enzyme preparations from NBT and TBT; 4) the parameters of the temperature inactivation of enzyme preparations at 45-52 degrees C, especially the change of entropy (delta S*) were different in the case of NBT and TBT; 5) a peptide fraction isolated from sheep brain differently inhibited the Na,K-ATPase from NBT and TBT. In conclusion, these data demonstrate that there are significant differences in functioning of Na,K-ATPase from NBT and TBT, and that besides lipid-protein interactions the local domenic conformational changes in the enzyme molecule may play a definite role in these differences.

[Characteristics of cooperative binding of Na+ and K+ with Na+,K+-ATPase depending upon its oligomeric structure]. / Osobennosti kooperativnogo sviazyvaniia Na+ i K+ s Na+,K+-ATPazoi mozga v zavisimosti ot ee oligomernoi struktury.

It has been shown that the desensibilization of the enzymic preparations of Na+, K+-ATPase by urea, DS-Na, digitonin and CHAPS reduces differently the amount of alpha beta-protomer in the enzymic preparations and the Hill coefficients of Na+ and K+. The factors (urea, DS-Na) which cause a more pronounced decrease in the amount of beta-protomer reduce the nH of Na+ for Na+, K+-ATPase and nH of K+ for Na+, K+-ATPase and K+-pNPPase to unit. The analysis of the effects of ATP and pNPP indicates that ATP has a protective effect only in the case of urea and DS-Na, but this effect is not exerted by pNPP (nonallosteric substrate). A conclusion is drawn that cooperative interactions of Na+, K+-ATPase from the brain with Na+ require more higher level of the oligomeric structure of enzyme than cooperative interactions with K+. At the same time these cooperative interactions in the both cases need subunits interactions in the protomer and interactions between cation sites with relatively high affinity.

[Features of temperature dependence of the Na+,K+-ATPase reaction in normal and tumorous brain tissue]. / Osobennosti temperaturnoi zavisimosti Na+,K+-ATP-aznoi reaktsii v normal'noi i opukholevoi tkani mozga.

It has been shown that in the enzyme preparations (EP) from normal brain tissue (NBT) a typical break on the Arrhenius plot appeared at 20-22 degrees C, nH for Na+ and K+ exceeding 1.7 and 1.4, respectively. In EP from tumoural brain tissue (TBT) no break on the Arrhenius plot at 20-22 degrees C was revealed, but it appeared at 27.5 + 30.5 degrees C. The nH for Na+ with Na+,K+-ATPase from TBT was only 0.9, but the cooperative binding of K+ was preserved (nH = 1.3). Electrophoregrams (EP) from TBT showed additional protein bands. The urea and digitonin treatment of EP from NBT induced a break on the Arrhenius plot at 27.5-30.5 degrees C. It is suggested that the break at 27.5-30.5 degrees C is, probably, accompanied by local changes in the conformation of protein components of the enzyme.

[Comparative characteristics of the distribution and various properties of Na,K-ATPase from human and rat gastric mucosa]. / Sravnitel'naia kharakteristika raspredeleniia i nekotorykh svoistv Na,K-ATPazy slizistoi obolochki zheludka cheloveka i krysy.

Subcellular fractions were isolated from homogenates of human and rat gastric mucosal membranes by means of differential centrifugation; the highest Na+, K(+)-ATPase activity was detected in microsomal fraction. The enzymatic activity was higher in human gastric mucosal membrane as compared with the rat tissue. Na+, K(+)-ATPase activity was inhibited by 0.1% SDS added into the homogenization mixture. Ouabain 1.5 x 10(-3) M did not affect the enzymatic activity. The enzyme had a pH optimum in both these tissues at pH 7.2 = 7.4 in 30 mM imidazol-HCl buffer and at pH 7.1-7.2 in 40 mM Tris-HCl buffer. K+ exhibited maximal activating effect at 20 mM concentration in human gastric mucosal membrane and at 5 mM concentration in rat tissue. The ratio ATP/Mg2+ as 1:1 proved to be optimal at 2 mM concentration.

[Relation between the protein composition of glial tumors and various clinico-morphologic indices]. / Zavisimost' belkovogo sostava glial'nykh opukholei ot nekotorykh kliniko-morfologicheskikh pokazatelei.

The work was concerned with the study of 57 gliomas, among which were 30 glioblastomas, 20 astrocytomas, and 7 oligodendrogliomas. Specimens collected from 26 patients who underwent operation for severe craniocerebral trauma, meningioma, and carcinoma metastasis were examined as controls. The proteins of the tumor tissues and those of the brain matter surrounding the tumor and of normal brain matter were fractionated in polyacrylamide gel. It was found that the amount of water soluble protein, both in the total protein content and in all its fractions, was much greater in the glial tumors than in normal brain matter. The effect of 11 factors on the tissue protein composition was studied by factor analysis. The histological structure and extent of vascularization of the tumor as well as the presence of intracranial hypertension were found to produce the highest effect on the fractional distribution of the proteins.

[Kinetics of the inactivation of muscarinic cholinoreceptors by solubilized digitonin]. / Kinetika inaktivatsii soliubilizirovannogo digitoninom muskarinovogo kholinoretseptora.

The kinetics of spontaneous inactivation of the digitonin-solubilized rat brain muscarinic cholinoreceptor was investigated at 4 degrees, 15 degrees, 25 degrees, 35 degrees and 45 degrees C. The inactivation process was followed by the loss of specific L-[3H] quinuclidinyl benzilate binding capacity after incubation of the receptor at an appropriate temperature. Since the inactivation process of the receptor inactivation obeys the first order kinetics, it was possible to determine the values of inactivation rate constants (kappa in). It was shown that the inactivation rate does not depend on the detergent excess in a reaction mixture and is characterized by the apparent activation energy, Ea = 158 +/- 7 . KJ/mole and entropy, delta S not equal to = 249.8 J/K . mole. These values are in good agreement with those obtained for the water-soluble proteins, but differ essentially from the analogous values for the spontaneous activation of the membrane-bound receptor.