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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.

Metal ions play vital roles in enzymes. They may also show sensitivity to various sulfhydryl reagents and chelating reagents. Effect of some metal ions, EDTA and sulfhydryl reagents on the activity of partially purified β-amylase of radish root were studied. Amylolytic activity of purified enzyme was increased substantially in the presence of Ca2+, Mg2+, and Zn2+. Some other divalent cations Cu2+, Pb2+, Sn2+, and Hg2+ almost completely ceased the enzyme activity. Cobalt (II), Manganese (II), and Iron (III) exhibited moderate activating effects on the activity. Of the monovalent cations, Na+ and Ag+ reduced the β-amylase activity, while K+ increased. The chelating agent EDTA was found to be effective in the enzyme. Sulfhydryl reagents, Iodoacetic acid and N-Ethylmaleimide showed marginal inhibitory effect, but p-hydroxymercuribenzoic acid (PCMB) almost completely stopped the enzyme activity. The addition of thiol compounds such as cysteine could reverse the inhibitory effect of heavy metals and PCMB. The results indicate that sulfhydryl groups of radish root β-amylase were essential for the activity although it is not clear whether the sulfhydryl groups were directly involved in catalysis.