ELECTROKINETIC CHARACTERIZATION OF IMMOBILIZED ASPERGILLUS-NIGER BETA GALACTOSIDASE

Microcrystalline cellulose was activated with diphenylmethane 4,4-diisocyanate and triethylamine and was used to immobilize beta-galactosidase (beta-Gal) at 4 or 20C and pH 3.6 or 4.6. The activation procedure modified the electrokinetic characteristics of the carrier, making the zeta potential less negative; at pH below 4.5 the zeta potential became positive. Immobilization of beta-Gal shifted the isoelectric point to acid pH. Conditions to produce the highest residual beta-Gal activity were pH 4.6 and temp. of 4C. Addition of 1250 p.p.m. NaCl, CaCl2 or Ca(NO3)2 at the optimum pH decreased beta-Gal activity, effects being greater for the immobilized enzyme than for free enzyme. Optimum pH after immobilization was increased by approx. one unit by Ca salts, while Na had no effect. Ca(NO3)2 caused a shift of zeta potential to more positive values and the isoelectric point of the immobilized enzyme to alkaline pH. Na had less influence on zeta potential but at 50 p.p.m. did displace the isoelectric point.