RESUMO
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.
Assuntos
Encéfalo/enzimologia , ATPase Trocadora de Sódio-Potássio/metabolismo , Trifosfato de Adenosina/farmacologia , Animais , Encéfalo/efeitos dos fármacos , Neoplasias Encefálicas/enzimologia , Carbodi-Imidas/farmacologia , Cloromercurobenzoatos/farmacologia , Humanos , Ouabaína/farmacologia , Conformação Proteica/efeitos dos fármacos , Ratos , Valores de Referência , ATPase Trocadora de Sódio-Potássio/antagonistas & inibidores , ATPase Trocadora de Sódio-Potássio/efeitos dos fármacos , Relação Estrutura-Atividade , TemperaturaRESUMO
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.
Assuntos
Neoplasias Encefálicas/enzimologia , Encéfalo/enzimologia , ATPase Trocadora de Sódio-Potássio/metabolismo , Animais , Encéfalo/efeitos dos fármacos , Neoplasias Encefálicas/metabolismo , Digitonina/farmacologia , Humanos , Cinética , Conformação Proteica , Ratos , Temperatura , Ureia/farmacologiaRESUMO
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.