Studies on the Decarboxylation of Pyruvate.II.Kinetic Studies on the Binding of Thiamine Pyrophosphate to Pyruvate Decarboxylase

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The reconstitution of pyruvate decarboxylase has been studied kinetically in thepresence of several concentrations of thiamine pyrophosphate (TPP) and Mn²⁺. The Km for TPP determined graphically was decreased by increasing Mn²⁺ concentration, while V_max was almost unchanged. The values of Kms for Mn²⁺ and V_max, were affected in mixed manner by the amount of TPP.
The significance of Kms thus determined is discussed and the values are compared to that determined in transketolase.