J. Biol. Chem., Vol. 265, Issue 11, 6074-6078, 04, 1990
Reaction of compound III of myeloperoxidase with ascorbic acid
LA Marquez and HB Dunford
Department of Chemistry, University of Alberta, Edmonton, Canada.
A relatively pure and stable compound III of bovine spleen myeloperoxidase
was prepared from native enzyme using the aerobic oxidation of
dihydroxyfumarate to generate O2-(.). Spectral scans show well defined
peaks at 450 and 625 nm and an isosbestic point between compound III and
native enzyme at 440 nm. Compound III decayed to native enzyme without any
detectable intermediate. The rate of decay was faster at alkaline pH values
and also in the presence of superoxide dismutase. Ascorbic acid reduces
compound III to native enzyme with a second order rate constant of (4.0 +/-
0.1) x 10(2) M-1 s-1. The ascorbic acid reduction of compound III has
potential physiological relevance since it could help maintain the
catalytic cycle of myeloperoxidase to generate the bactericidal agent
hypochlorous acid.