Metabolie control mechanisms in mammalian systems. XI Pyruvate kinase modulation in the rat prostate and seminal vesicles

The modulation of pyruvate kinase activity by several metabolites has been investigated in the prostate gland and seminal vesicles of normal mature rats. Whereas direct addition of fructose 1,6-diphosphate to the reaction mixture exerted no effect on pyruvate kinase activity, slight activation of the prostatic and seminal vesicular enzyme was produced by L-alanine. Pyruvate kinase activity in both accessory sexual tissues was rapidly inactivated by incubation of the supernatant fluids at 37 °C; this inactivation was prevented by L-alanine. Whereas L-phenylalanine was found to be a competitive inhibitor of prostatic and vesicular pyruvate kinase, L-alanine was capable of preventing and reversing the inhibition produced by L-phenylalanine. Pyruvate kinase activity in both tissues was also inhibited by Cu2+ in concentrations as low as 0.005 mM; 50% inhibition of the enzyme was produced by 0.2 mM Cu2+. Addition of L-alanine prevented as well as reversed the inhibition produced by low concentrations of this cation.The sulfhydryl inhibitor, p-CMB, produced a dose-dependent inhibition of prostatic and vesicular pyruvate kinase whereas addition of penicillamine resulted in a slight activation of the enzyme. In addition, penicillamine effectively reversed the inhibition produced by p-CMB as well as by Cu2+. The thermal inactivation of pyruvate kinase activity in accessory sexual tissues was also prevented effectively when the supernatant fluids were preincubated in the presence of penicillamine.