[Interaction of thiamine pyrophosphate and some of its analogs with the pyruvate dehydrogenase complex from the...

Highly purified preparations of the pyruvate dehydrogenase complex from bovine adrenals partially contain strongly bound thiamine pyrophosphate (TPP) which provides to 35% of the maximal activity measured under saturation with the exogenous TPP. The dependence of the complex-catalyzed reaction rate on the TPP concentration is described by Michaelis-Menten equation. The apparent value of Km for TPP without Mg2+ is 2.3 mumol. Magnesium ions reduce Km to 1.1 mumol. The constant of the TPP with the enzyme association rate calculated by the lag-period without Mg2+ is 3043 mol-1 s-1 in the presence of Mg2+ it is 9090 mol-1 . s-1. Phosphorus ethers of oxy- and tetrahydrothiamine produce a competitive type inhibition on the pyruvate dehydrogenase complex with respect to TPP. Oxythiamine pyrophosphate (Ki--0,07 microM) and tetrahydrothiamine pyrophosphate (Ki--0,1 microM) possess the highest inhibitory action.