[The role of Ca++ in regulation of oxoglutarate dehydrogenase complex activity from bovine adrenal cortex].

Binding of Ca2+ ions by EGTA is established to increase the oxoglutarate dehydrogenase complex K'm for 2-oxoglutarate up to 25 mM in spite of the Mg2+ ions presence in the medium. The maximum reaction rate remains unchanged. Addition, besides EGTA of an equimolar Ca2+ amount to the medium induces a more than 100-fold decrease in K'm. A positive effect of Ca2+ ions is intensified by ADP. Ca2+ counteracts the inhibition of the oxoglutarate dehydrogenase complex activity by NADH. When chelating Ca2+ by EGTA with NADH available, a nonhyperbolic dependence of the reaction rate on the 2-oxoglutarate concentration is observed. When Ca2+ is absent, signs of a positive cooperative interaction of the enzyme with ADP and NADH are observed under conditions when 2-oxoglutarate concentration is much lower than the saturating one.