Alteration of substrate regulation patterns in glutamate dehydrogenase by enzyme immobilization

Substrate regulation patterns were changed by covalent binding of bovine liver glutamate dehydrogenase via primary amino groups to CNBr- and CH-activated Sepharose 4B. Lineweaver-Burk plots show that the NAD activation region changed from being abrupt to elongated when the enzyme was immobilized to either support. The elongated region contains two inflection points and resembles substrate activation of several other allosteric oligomers. Glutamate induced varying degrees of abrupt activation in immobilized glutamate dehydrogenase and inhibited the native enzyme. This activation is characterized by an activation threshold, an increase in the apparent dissociation constant, and a correlation between the apparent rate constant and the degree of activation. These three features characterize other glutamate dehydrogenase systems.