[Different efficiency of Mn2+, Ca2+ and Mg2+ ions, in the reaction of the pyruvate dehydrogenase complex of adrenal glands with thiamine pyrophosphate].

In systems with pyruvate dehydrogenase complex from bovine adrenal glands and endogenous residual thiamine pyrophosphate (TPP), Mn2+, Ca2+ and Mg2+ decreased the lag period and increased the rate of steady-state reaction. Relative efficiency of the cations was the following: Mn2+ greater than Ca2+ greater than Mg2+. The activating effect of these cations was also exhibited in presence of low content of exogenous TPP but it was not found under conditions of saturation of pyruvate dehydrogenase complex with the coenzyme. In the systems with the cations concentrations approaching the optimal ones, the apparent Km value for TPP in the presence of calcium was about 4-fold and in presence of manganese about 7-fold lower as compared with the systems containing magnesium.