[Cooperative interaction of pyruvate dehydrogenase from pigeon breast muscle]

Cooperative interaction of pyruvate with the pyruvate dehydrogenase (PD) complex from pigeon breast muscle was shown. The sigmoidal dependence of the reaction rate on pyruvate concentration was observed for the PD complex. The Hill coefficient is equal to 1,5; no inhibition by the substrate (up to 2.2.10(-3) M) was found. The kinetic behaviour of the isolated pyruvate dehydrogenase component (PDH) analyzed under similar conditions, is more complex; this may be probably due to the presence of oligomeric forms with different molecular weights and specific activities. The competitive inhibitor of the PD complex--an amide of pyruvic acid (PA) (Ki=6.3-10(-6) M) activates the enzyme at low concentrations (less than 2,10(-6) M). When PA is present, the dependence of the reaction rate on pyruvate concentration gives a usual hyperbolic curve, v of [S]o. It is concluded that pyruvate may have a regulatory effect on the activity of muscle PD complex.