Biochemical characterization of a purified arginase from the gut of Oryctes rhinoceros larvae

Abstract

Arginase acts as a mediator in the final phase of the urea cycle, protecting against excessive ammonia under homeostatic conditions by producing L-ornithine and urea. In this study, the physicochemical properties of Oryctes rhinoceros Larva arginase were investigated for biochemical comparison with its well-studied terrestrial mammalian. Oryctes rhinoceros larva arginase was isolated and purified to homogeneity. The purification procedure involved ion-exchange chromatography on DEAE-cellulose and affinity chromatography on reactive Blue 2-agarose. The pure enzyme had a specific activity of 38.7 U/mg, a purification fold of 63.4, and a percentage yield of 16.5%. O. rhinoceros gut arginase had a native and subunit molecular weight of 82 and 45 kDa, respectively and the K_m and V_max were 11.25 mM and 13.055 μmmol/min/mL, respectively. The activity was optimum at 60 °C m max (pH 8). The enzyme retained more than 60% of its activity at 50 °C for 60 min. The inhibition study on the enzyme showed that cations salts (CaCl₂ , BaCl₂ , HgCl₂ , and SnCl₂ ) enhanced the enzyme activity at 1 mM concentration except for SnCl₂ . EDTA, a chelating compound, strongly inhibited the activity of the enzyme. The 2 effect of different amino acids on activity showed that L-valine, L-serine, L- aspartic acid, and L-glutamic acid had a moderate inhibitory (60%, 63%, 65.4%, 69.1%, respectively) effect on the enzyme activity. The study concluded that there were similarities between O. rhinoceros larva arginase and those of other ureotelic animals in terms of kinetics and physicochemical properties.