Urease was used for estimation of $Cu^{2+}$ in aqueous solution. Process variables were optimized by Central Composite Design using MINITAB$^{(R)}$ 15 software. Results predicted by the design were close to experimental value indicating suitability of the model. 3D surface plot and isoresponse contour plot were helpful in predicting results by performing limited set of experiments. Urease was extracted from discarded seeds of pumpkin to apparent homogeneity by heat fractionation and gel filtration. Homogeneous enzyme preparation was further immobilized in 3.5% alginate. Effect of $Cu^{2+}$ on the activity of soluble and immobilized enzyme was investigated. Enzyme inhibition was biphasic, irreversible, and non-competitive (Ki = 1.06 ${mu}M$).