Abstract

Arginase (EC 3.5.3.1) catalyzes the hydrolysis of arginine to ornithine and urea. The role of arginase in insect has been seen in the growth of insect at various stages of development and energy requirement for flight. Here, we reported the properties of arginase in the gut of adult cockroach, Periplaneta americana. The enzyme was partially purified with ammonium sulphate precipitation and affinity chromatography. The specific activity of the arginase was 3.0 µmol/min/mg of protein. The Michealis (K_m) constant was 0.33 mM and the arginase preferred arginine as substrate. The optimum pH was 7.0, while the optimum temperature was 80°C. The ascorbic acid, reduced glutathione (GSH) and 2-mercaptoethanol completely inactivated the enzyme. The amino acids: lysine, valine, serine, and asparagine showed moderate inhibition (with residual arginase activities of 81.7, 96.1, 96.9 and 97.0%, respectively), while proline and cysteine (>100%, respectively) stimulated the arginase activity. The cations: Sn²⁺, Hg²⁺, Ni²⁺ and Co²⁺ showed slight inhibition on the enzyme. The enzyme was markedly enhanced by Zn²⁺ and Mg²⁺.

Key words: Arginase, insect gut, cockcroach, characterization.