Lipoamide dehyrogenase immobilized on porous glass

Lipoamide dehydrogenase (NADH:lipoamide oxidoreductase, EC 1.6.4.3) isolate from pig heart and Escherichia coli was covalently coupled by both diazonium and amide bonds to controlled pore glass beads (96% silica). When the enzyme was immobilized in the presence of NAD+, the enzyme no longer exhibited its normal requirement for NAD+ for full activity. If the immobilized enzyme was then treated with NADase, the requirement for NAD+ was restored. Enzyme immobilized in the absence of NAD+ exhibited normal NAD+ dependence both prior to an after NADase treatment. These results are discussed in terms of co-immobilization of NAD+ at or near the allosteric site of the enzyme.