Active site chlorination of D-amino acid oxidase by N-chloro-D-leucine

N-Chloro-D-leucine is an irreversible inhibitor or D-amino acid oxidase on a time scale of seconds. Studies with N-[36C]chloro-D-leucine, N-chloro-D-[1-14C]leucine and N-chloro-D-[4,5-3H]leucine show that the modified enzyme has been chlorinated at a site, or sites, on the apoenzyme. The 36Cl measurements agree with titrations of catalytic activity in showing that two chlorine equivalents are incorporated per active site flavin. Kinetically, the interaction with N-chloro-D-leucine behaves in a manner which is consistent with consecutive chlorinations of an amino acid residue, or residues, in the active site region by the first 2 molecules of N-chloro-D-leucine to be processed by the enzyme. The effect of chlorination of the enzyme on the steady state parameters for oxidation of D-alanine is entirely explained by a single perturbation, namely, a 1000-fold reduction in the specific rate of flavin reduction as measured directly by rapid reaction techniques.