Inactivation of Bovine Glutamate Dehydrogenase by Carbamyl Phosphate and Cyanate

By kinetic studies and the identification of the labeled peptide of the [14C]KNCO-modified protein, the inactivation of bovine liver glutamate dehydrogenase by potassium cyanate can be attributed to the carbamylation of the e-amino group of lysine-97. Although the e-amino group of lysine-97 is the major site of carbamylation by cyanate, the α-amino group of alanine-1 and e-amino group of lysine-85 are also sites of carbamylation. Kinetic experiments indicate that the apparent pKa of the reactive amino group is 7.7, a value which is in good agreement with the apparent pKa of 8.0 ± 0.3 obtained by studies of the inactivation of the enzyme by reaction with pyridoxal and pyridoxal phosphate. Experimental evidence suggests that the previously reported inactivation of glutamate dehydrogenase by carbamyl phosphate can be attributed to the cyanic acid which is formed by the decomposition of carbamyl phosphate.