[Effect of different levels of carbonic acid on glutamate dehydrogenase activity]

The initial rate of direct and reverse reactions catalyzed by crystalline NAD(P)+-dependent glutamate dehydrogenase from bovine liver as well as Km, V and some other kinetic parameters were studied as affected by carbonic acid in different concentrations (0, 10, 20, 40, 60 mM) at p Hof the incubation media 6.4-9.1. It is shown that the dependence of the initial rate on pH both of the direct and reverse reactions varies with the carbonic acid concentration. In the pH alkaline range the glutamate dehydrogenase activity is inhibited in the presence of a mixture of HCO3 and pCO2 (soluble carbonic acid) and in the acid range pH it has a tendency to increase. The pKb value lowers by an order and the pKa value remains practically unchanged. The interaction of pCO2 with E-amino group of the lysin residue in the enzyme molecule accompanied by formation of carbamate is supposed to be possible. The bicarbonate ion may also affect the enzyme.