Brain Succinic Semialdehyde Dehydrogenase; Reaction of Arginine Residues Connected with Catalytic Activities

The succinic semialdehyde dehydrogenase from bovine brain was inactivated by treatment with phenylglyoxal, a reagent that specifically modifies arginine residues. The inhibition at various phenylglyoxal concentrations shows pseudo-first-order kinetics with an apparent second-order rate constant of 30 M^-1min^-1 for inactivation. Partial protection against inactivation was provided by the coenzyme NAD⁺, but not by the substrate succinic semialdehyde. Spectrophotometric studies indicated that complete inactivation of the enzyme resulted from the binding of 2 mol phenylglyoxal per mol of enzyme. These results suggest that essential arginine residues, located at or near the coenzyme-binding site, are connected with the catalytic activity of brain succinic semialdehyde dehydrogenase.