Author(s): Om Prakash, Mahe Talat, S H Hasan, Rajesh K Pandey
Enzyme urease is extracted from the discarded seeds of pumpkin. Urease was purified to apparent homogeneity (5.2 fold) by heat treatment at 48 ± 1°C and gel filtration through Sephadex G-200. Effect of model metal ions on the activity of the homogeneous enzyme preparation (sp. activity 353 U/mg protein, A280/A260 = 1.12) of soluble as well as immobilized enzyme was investigated. The soluble and immobilized urease has been used for the quantitative estimation of general water pollution with heavy metal ions like Hg2+, Cu2+, Cd2+, and Co2+. The measurements of the urease residual activity have been carried out in tris-acetate buffer after pre-incubation of model metal salt. The inhibition was found to be biphasic with an initial rapid loss of activity and remainder in slow phase of 10∼15 min. The immobilization was done in 3.5% alginate beads leading to 86% of entrapment. There was no leaching of the enzyme over a period of 15 days at 4°C. The beads were fairly stable up to 50°C and exhibited activity even at −10°C. The inhibition by these ions was non-competitive and irreversible, hence could not be restored by dialysis. Based on the values of inhibition constant Ki the heavy-metal ions were found to inhibit urease in the following order Hg2+ > Cu2+ > Cd2+ > Co2+.