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

Pigeonpea (Cajanus cajan) urease was immobilized on 1 cm x 1 cm DEAE-cellulose paper strips. The optimum immobilization (51% activity) was observed at 4degreesC, 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 67degreesC, compared with 47degreesC 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 (K-m) for the DEAE-cellulose-immobilized urease was found to be 4.75 mM, 1.5 times higher than the soluble enzyme. Immobilized strips stored at 4degreesC showed an increased half-life (t(1/2) = 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(R) (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.