L-alanine:An activator of pyruvate kinase in the rat prostate

L-alanine when added directly to the reaction mixture produced an activation of prostatic pyruvate kinase whereas fructose 1,6-diphosphate failed to exert any significant effect on the enzyme activity. The activating effect of L-alanine on pyruvate kinase was observable at 5 mM concentration although, maximal activation was produced by 50 mM alanine. Activation of the prostatic enzyme was observed even at low concentrations of the substrate, phosphoenolpyruvate. L-alanine was also effective in protecting prostatic pyruvate kinase against thermal inactivation. Higher concentrations of phosphoenolpyruvate resulted in progressive inhibition of the activity of pyruvate kinase in the prostate. Activation by L-alanine was demonstrable even when the enzyme activity was markedly inhibited by high concentrations of the substrate. The results obtained indicate that pyruvate kinase in the rat prostate might differ in its kinetic properties from the hepatic enzyme since the latter is activated by fructose 1,6-diphosphate, inhibited by L-alanine and is known to remain unaffected by high concentrations of phosphoenolpyruvate.