Immobilization of pigeonpea (Cajanus cajan) urease on DEAE-cellulose paper strips for urea estimation

Pigeonpea (Cajanus cajan) urease was immobilized on 1 cm*1 cm DEAE-cellulose paper strips. The optimum immobilization (51% activity) was observed at 4 (degree)C, with a protein concentration of 1.0 mg/strip. The apparent optimum pH shifted from 7.3 to 6.8. Immobilized urease showed an optimal stability temperature of 67 (degree)C, compared with 47 (degree)C for the soluble urease. Time-dependent kinetics of the thermal inactivation of the immobilized urease were examined and found to be monophasic as compared with the soluble enzyme, which was biphasic. The Michaelis constant (Km) for the DEAEcellulose-immobilized urease was found to be 4.75 mM, 1.5 times higher than the soluble enzyme. Immobilized strips stored at 4 (degree)C showed an increased half-life (t1/2=150 days). There was practically no leaching of the enzyme from the immobilized strips over a period of 2 weeks. These strips were used for estimating the urea content of blood samples; the results obtained matched well with those obtained in a clinical laboratory through an Autoanalyzer (Zydus Co., Rome, Italy). The easy availability of pigeonpea urease, the ease of its immobilization on DEAE-cellulose strips and the significantly lower cost of urease described in the present study makes it a suitable product for future applications in diagnostics.