The kinetics of inhibition of Vigna catjang cotyledon and buffalo liver arginase by L-proline and branched-chain amino acids

The effect of proline, isoleucine, leucine, valine, lysine and ornithine under standard physiological conditions, on purified Vigna catjang cotyledon and buffalo liver arginases was studied. The results showed that V. catjang cotyledon arginase is inhibited by proline at a lower concentration than buffalo liver arginase and the inhibition was found to be linear competitive for both enzymes. Buffalo liver arginase was more sensitive to inhibition by branched-chain amino acids than V. catjang cotyledon. Leucine, lysine, ornithine and valine are competitive inhibitors while isoleucine is a mixed type of inhibitor of liver arginase. We have also studied the effect of manganese concentration which acts as a cofactor and leads to activation of arginase. The optimum Mn2+ concentration for Vigna catjang cotyledon arginase is 0.6 mM and liver arginase is 2.0 mM. The preincubation period required for liver arginase is 20 min at 55 degrees C, the preincubation period and temperature required for activation of cotyledon arginase was found to be 8 min at 35 degrees C. The function of cotyledon arginase in polyamine biosynthesis and a possible role of branched chain amino acids in hydrolysis of arginine in liver are discussed.