Ion exchange immobilization of changed β‐galactosidase fusions for lactose hydrolysis

The use of charged peptides fused to enzymes for immobilization onto ion‐exchange membranes was explored for the enzyme ×‐galactosidase. The additional charged peptides, containing 1, 5, 11, and 16 aspartates, fused to ×‐galactosidase, for the most part did not interfere with the kinetic behavior for lactose hydrolysis. There was a 2‐fold decline in V m for the 16‐aspartate fusion, but the others were quite similar to the wild type enzyme (BGWT). BGWT and the fusions all retained approximately 50% of their activities when adsorbed onto ion‐exchange membranes. In contrast to BGWT, the enhanced binding strength of the 11 aspartate fusion provided the ability to hydrolyze whey permeate at 0.3 M ionic strength without enzyme leakage, and to immobilize the enzyme directly from diluted cell extract with 83% purity. © 1994 John Wiley & Sons, Inc.