Cooperation of Divalent Ions and Thiamin Diphosphate in Regulation of the Function of Pig Heart Pyruvate Dehydrogenase Complex

Abstract

The role of Mg²⁺, Cat +, and Mn²⁺ in regulation of purified pig heart pyruvate dehydrogenase complex (PDC) containing endogenous thiamin diphosphate (TDP) was studied. It was found that the effects of the cations depended on the presence of exogenous TDP. In the absence of added TDP, the divalent cations led to a shortening of a lag phase of the PDC reaction and a strong reduction of the Km value for pyruvate. The relative effi-ciency of the three types of ions are presented as follows: Mn²⁺>Ca²⁺>Mg2t The other sources claim that in the presence of exogenous TDP, which alone strongly increased the affinity of PDC for pyruvate, any significant additional effects of the cations were not ob-served. However, Mg²⁺, Ca²⁺, and Mn²⁺ decreased the Km value for CoA in both cases, the absence and presence of exogenous TDP, in approximately a similar extent (about twofold), The affinity of PDC for NAD+ seems to be not sensitive to the presence of the divalent cations. The data obtained suggest that Mg²⁺, Ca²⁺, and Mn²⁺ can cooperate with TDP as positive regulatory effectors of pig heart PDC on the level of pyruvate dehydrogenase and lipoamide acetyltransferase components of the complex.