The use of charged peptides fused to enzymes for immobilization onto ion-exchange membranes was explored for the enzyme beta-galactosidase, The additional charged peptides, containing 1, 5, 11, and 16 aspartates, fused to beta-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.