Radiolabeling of a wound-inducible pyridoxal phosphate-utilizing enzyme: Evidence for its identification as ACC synthase

1-Aminocyclopropane-1-carboxylic acid (ACC) synthase, a pyridoxal phosphate-utilizing enzyme, catalyzes the conversion of S-adenosylmethionine to ACC, the rate-limiting step in the biosynthesis of the plant hormone ethylene. We report the partial purification (400-fold) of ACC synthase from wounded pink tomato pericarp. Further purification results in a decrease in specific activity apparently due to the instability of the enzyme. Radiolabeling of a pyridoxal phosphate-utilizing protein in the ACC synthase-enriched fraction was achieved by reduction using tritiated sodium borohydride. Evidence that this radiolabeled protein is ACC synthase is presented.