Incubation of an NAD + -dependent succinic semialdehyde dehydrogenase from bovine brain with 4-dimethylamino-azobenzene-4-iodoacetamide (DABIA) resulted in a time-dependent loss of enzymatic activity. This inactivation followed pseudofirst-order kinetics with a second-order rate constant of 168M )1 Æmin )1 .The spectrumofDABIA-labeled enzyme showed a characteristic peak of the DABIA alkyl-ated sulfhydryl group chromophore at 436 nm, which was absent from the spectrum of the native enzyme.
