Biochemical Studies of Urease From Pigeonpea ( Cajanus Cajan)

Abstract

The urease (urea amidohydrolase; EC 3.5.1.5) was isolated from the mature seeds of pigeonpea (Cajanus cajan). The pigeonpea urease was characterized biochemically and inhibition studies were undertaken. The enzyme was stored at two different temperatures, 4°C & 37°C, and it was found that the t 112 was 60 days at 4°C whereas t 112 was 15 days when stored at 37°C. Under steady state kinetics, the optimum. pH & optimum temperature were found to be 7.3 and 70°C, respectively. The values of K111 and V,11ax were 20.4 mM and 0.625 ~unol NH3/min/mg, respectively. Thermal inactivation studies of pigeonpea urease revealed a variation in the kinetic pattern at different temperatures. At 50°C & 60°C, the enzyme showed almost no loss in its kinetic potential over a period of 35 min. However, at higher temperatures (60°C & 70°C) the pattern was biphasic. The inactivation studies strongly favour the oligomeric nature of urease. *The fsn value for boric acid was found to be 7.6 mM and the K1 was 1.10 mM. The competitive type of inhibition was recorded. Furthermore, NaCl showed poor inhibition potency (!5o = 205 mM). The fso value for Hg2+ was recorded at 6.10 nM; revealing its highest inhibition potency. The inhibition studies are important due to many factors. Elevated levels of soil microbial urease have been known to decrease the efficiency of urea fertilizers. It is speculated that the low concentration used for the inhibitors can also inhibit any of the soil ureases, which is important in plant agronomy. Thus such studies may have medical or agronomic importance, as well as provide insight into the urease catalytic mechanism. Keywords: Urease; Boric acid; Pigeonpea; Inhibiton; Cajanus cajan