effects of some environmental variables on urease in germinating chickpea (cicer arietinum l.) seed

Abstract

Enzyme activity is influenced by a large number of factors. Environmental conditions such as pH, temperature, salt concentration, substrate concentration, activators, and inhibitors may change the three dimensional shape of an enzyme, altering its rate of activity and/or its ability to bind substrate. The effects of such environmental factors were evaluated. The optimum pH and temperature of the purified urease were 7.2 and 48°C, respectively, using urea as substrate. The optimum substrate (urea) concentration for urease was 25 mM. The enzyme showed the highest activity when incubated for 30 min at 480C. EDTA, a metal chelator, decreased the enzyme activity significantly. This may be due to the removal of metal ions located on or near the active site. Divalent cations like Ba2+ and Mg2+ slightly stimulated the enzyme at a concentration of 1-3 mM whereas Na+ and K+ produced little or no effect on the activity. Ca2+ enhanced urease activity by 120.47%, while Pb2+, Cu2+, Zn2+ and Hg2+ almost completely inhibited the urease activity.