Comparison of the kinetic properties of the pyruvate dehydrogenase complex from pig kidney cortex and medulla

The activity of the pyruvate dehydrogenase complex (PDC) purified from pig kidney medulla was affected by K+, Na+, CI", HCO3"", HP042" and changes in ionic strength. Increased ionic strength influenced the activity of PDC from medulla by decreasing the Vmax and S0.5 for pyruvate and increasing the Hill coefficient. The magnitude of these changes was smaller than the corresponding changes for PDC purified from the cortex. In the presence of K+ (80 mM), Na+ (20 mM), Cl~ (20 mM), HCO3" (20 mM), HPO42" (10 mM) and at ionic strength of 0.15 M the S0.5 for pyruvate of PDC from medulla was 117 nM and the enzyme complex was saturated by 1.1 mM pyruvate. Under these conditions the S0.5 for pyruvate of PDC derived from cortex was 159 nM and the enzyme was saturated at 4.5 mM pyruvate.