Partial Purification and Characterization of the Maize Mitochondrial Pyruvate Dehydrogenase Complex

The pyruvate dehydrogenase complex was partially purified and characterized from etiolated maize (Zea mays L.) shoot mitochondria. Analysis by sodium dodecyl sulfate-polyacrylamide gel electrophoresis showed proteins of 40, 43, 52 to 53, and 62 to 63 kD. Immunoblot analyses identified these proteins as the E1β-, E1α-, E2-, and E3-subunits, respectively. The molecular mass of maize E2 is considerably smaller than that of other plant E2 subunits (76 kD). The activity of the maize mitochondrial complex has a pH optimum of 7.5 and a divalent cation requirement best satisfied by Mg²⁺. Michaelis constants for the substrates were 47, 3, 77, and 1 μm for pyruvate, coenzyme A (CoA), NAD⁺, and thiamine pyrophosphate, respectively. The products NADH and acetyl-CoA were competitive inhibitors with respect to NAD⁺ and CoA, and the inhibition constants were 15 and 47 μm, respectively. The complex was inactivated by phosphorylation and was reactivated after the removal of ATP and the addition of Mg²⁺.