Comparative immunochemical studies of sulfite oxidases of vertebrate livers.

1. The sulfite oxidases from various vertebrates, including rat, rabbit, chicken, frog, and eel, were partially purified and their physiochemical, kinetic, and immunochemical properties compared. The physicochemical and kinetic properties of these five enzymes were similar. 2. Antibody against the molybdenum-containing peptide prepared from purified rat liver sulfite oxidase was raised in rabbits. In Ouchterlony double diffusion and quantitative immunoprecipitation tests, the antibody could form precipitates with the enzymes from rats and rabbits, but no reaction was observed with enzymes from other sources. 3. The sulfite-cytochrome c reductase activity of the enzymes from these five animals were inhibited by the antibody, though the enzymes from chicken, frog, and eel were less sensitive to the antibody than those from rat and rabbit. 4. The inhibition of binding between 3H-labeled rat sulfite oxidase and its antibody by unlabeled enzymes from other animals demonstrated that 10 to 20% of the antibody could cross-react with these enzymes.