Allosteric Regulation of Enzymatic Reactions in a Transparent Inorganic Sol-Gel Material

Glutamate dehydrogenase is encapsulated in a transparent porous silicate matrix by using sol-gel techniques. The inorganic polymer is formed around the enzyme (MW > 300,000 D). The enzyme is active in the material, catalyzes the reaction of L-glutamate to 2-oxoglutarate and follows Michaelis-Menten kinetics. The allosteric regulators ADP and GTP inhibit or activate the reaction; at pH 6, GTP acts as a strong activator and ADP acts as an inhibitor. This system involves a complex series of interactions; the co-enzyme NAD⁺ is required for catalysis, large-scale conformational changes accompany the binding of the substrate and coenzyme to the enzyme, the activators/inhibitors must bind to the enzyme to regulate the reactions, and the substrates and products must diffuse through the matrix to and from the binding site. The influence of the unique matrix on the complex enzymatic system is discussed.