Thiamine pyrophosphate as an effector of 2-oxoglutarate dehydrogenase complex from European bison heart.

Abstract

The purified 2-oxoglutarate dehydrogenase complex (OGDC) from the European bison heart was near saturated with endogenous bound thiamine pyrophosphate (TPP). Exogenous TPP added to the full OGDC reaction medium decreased S0.5 for 2-oxoglutarate approximately 2.6-fold without any notable change in the maximum reaction rate. The TPP effect was observed in the presence of 1 mM ADP which alone is a strong positive allosteric effector of OGDC. At an unsaturating 2-oxoglutarate concentration the A50 value for TPP was approximately 0.05 mM. The ADP-like action of exogenous TPP was also found in the 2-oxoglutarate dehydrogenase (E1) reaction, determined in the presence of 2,6-dichlorophenoloindophenol as an electron acceptor.