Mg-ATPase is very important in living organisms. To better understand the molecular mechanism of Mg-ATPase activity, we applied the method of kinetic analysis of multi-sited enzyme systems; this is a suitable approach used for kinetic investigation of multi-sited enzyme systems. The study of Mg-ATPase has demonstrated: (1) It is a multi-sited enzyme system whose functional unit is minimum a dimmer; (2) Its substrate is MgATP, while free ATP and Mg(2+) appear to be the enzyme modifiers with a dual effect; (3) The enzyme system for MgATP has at least three sites: i.e., the essential activator, full inhibitor, and partial effect modifiers sites; (4) Mg-ATPase carries out Mg(2+) transport through the 1Mg(2+):1ATP stochiometry. Based on the results of these analyses, the kinetic scheme for Mg-ATPase has been developed.

We studied, in the rat brain, the synaptosomal and microsomal membrane fractions of Cl− ion-activated, Mg2+-dependent ATPase, satisfying the necessary kinetic peculiarities of transport ATPases, by a novel method of kinetic analysis of the multisite enzyme systems: (1) the [Mg-ATP] complex constitutes the substrate of the enzymic reaction; (2) the V = f(Cl−) dependence-reflecting curve is bell-shaped; (3) substrate dependence, V = f(S), curves at a constant concentration of free ligands (Mgf, ATPf, Cl−); (4) as known from the literature, in the process of reaction a phosphorylated intermediate is formed (Gerencser, Crit Rev Biochem Mol Biol 31:303–337, 1996). We report on the Cl-ATPase molecular mechanism and its place in the “P-type ATPase” classification.

The comparative analysis between two enzymes, Mg-dependent and Mg-independent HCO3(-) ATPases, were studied in synaptosomal and microsomal membrane fractions of albino rat brain, using the method of kinetic analysis of the multi-sited enzyme systems. Therefore, it can be inferred that Mg-dependent HCO3(-) ATPase belongs to the group of "P-type" transporting ATPases. Mg-independent HCO3(-) ATPase with its kinetic properties may be attributed to the group of "Ecto" ATPases.