Beef liver glutamate dehydrogenase: a study of the oxidation of various alternative amino acid substrates retaining the correct spacing of the two carboxylate groups.

1. Several glutamate analogues substituted at the beta- or gamma-carbon atoms have been tested as substrates for glutamate dehydrogenase. 2. The two gamma-methyl derivatives and DL-beta-methylglutamate give the same pH optimum (8.7) as L-glutamate, but show inhibition by ADP and activation by GTP as pH 8, unlike glutamate and like the monocarboxylic substrate L-norvaline, which gives a pH optimum of 10. 3. L-gamma-methyleneglutamate, the poorest substrate tested (0.28% of rate with glutamate) gives a high pH optimum (10), like norvaline, but shows marked activation by both ADP (13-fold) and GTP (27-fold). 4. Despite the correct dicarboxylate spacing, all the analogues were much poorer substrates than L-norvaline.