Isolation and kinetic properties of arginase in the gut of grasshopper ( Zonocerus variegatus Linn)

Abstract

Arginase (EC 3.5.3.1) catalyzes the hydrolysis of arginine to ornithine and urea. Arginase was purified and characterized from the gut of Zonocerus variegatus through DEAE-cellulose and biogel-P100 gel filtration chromatography. The specific activity of the enzyme was 3.7 µmoles/min per mg of protein and a yield of 14.7%. An apparent molecular weight of 143,000 daltons was estimated by gel filtration on biogel P-100. The Michaelis constant (K m) of the enzyme was 40 mM with arginine as substrate. The optimum pH was 8.0 and the optimum temperature was 40 o C for Z. variegatus arginase. The enzyme was stable up to 40 o C for 20 min and lost all of its activity at 80 o C. The enzyme was specific for arginine as substrate. The enzyme was strongly enhanced in the presence of Mn 2+ , Na + , NH 4 + and Hg 2+ showed similar activation. Ni 2+ and Zn 2+ slightly inhibited Z. variegatus. Chelating (EDTA, citrate, ascorbic acid and urea) and thio (2-mercaptoethanol and cystein) compounds inhibited the activity of arginase in Z. variegatus. While amino acids (proline, lysine, aspartate and valine) showed no inhibition on arginase activity. The presence of arginase in the gut of Zonocerus variegatus could be for other functions rather than urea production in urea cycle.