[Characteristics of cooperative binding of Na+ and K+ with Na+,K+-ATPase depending upon its oligomeric structure]

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.