Superoxide production by an unusual aldehyde oxidase in guinea pig granulocytes. Characterization and cytochemical localization.

An aldehyde oxidase extracted from guinea pig granulocytes with isotonic KCl catalyzes the oxidation of a variety of aliphatic aldehydes and 2-OH-pyrimidine. The stoichiometry of the oxidation of 2-OH-pyrimidine is consistent with the reaction 2-OH-pyrimidine + OH- + O2 leads to uracil + H2O2. Between 75 and 90% of the peroxide produced results from dismutation of superoxide formed as an intermediate. The Km for 2-OH-pyrimidine is approximately 1.65 mM and the maximum velocity is 22.9 +/- 5.5 S.D. nmol of superoxide/min/10(7) cells. This same maximum velocity is observed for the substrates isobutyraldehyde, propionaldehyde, and acetaldehyde. Unlike other aldehyde oxidases, this enzyme is inactive with purines as substrates and is insensitive to antimycin A, menadione, and Triton X-100. The enzyme is inhibited by cyanide, methanol, and arsenite. The apparent molecular weight is approximately 340,000 +/- 25,000 and the pH optimum is in the range of 7.5 to 9.0. Electron cytochemistry reveals an association of this oxidase with the phagosome membrane. The potential significance of this oxidase is discussed in relation to microbicidal mechanisms.