Immobilization of L-glutamate dehydrogenase into soluble cross-linked polymers. ADP effect and electron microscopy...

Active soluble cross-linked L-glutamate dehydrogenase (L-glutamate: NAD(P)+ oxidoreductase (deaminating), EC 1.4.1.3) albumin polymers were produced. Electron microscopic studies and kinetic properties were studied with the polymer in solution and compared with previous published data about the enzyme immobilized inside proteic films (Barbotin, J.N. and Breuil, M. (1978) Biochim. Biophys. Acta 525, 18--27). The glutaraldehyde effect on activity yield, ADP and beta-NAD+ protection, stability and pH rate profile were studied and discussed. Apparent Michaelis constants were determined with soluble polymers produced with or without ADP during the grafting process. Experiments were performed on the regulatory properties of immobilized glutamate dehydrogeanse showing the decrease of ADP activation and GTP inhibition as compared to the free form. In other respects, electron microscopy observations showed morphological differences between the two populations of soluble polymers produced in presence of ADP, obtained after gel filtration on Sepharose 6B. Linear aggregates of high molecular weight and classical soluble polymers were obtained. Similar Km values and regulatory properties were exhibited by the two forms, demonstrating the absence of interdependence between the allosteric control and the polymerization of enzyme monomers.