BENZOIC-ACID 2-HYDROXYLASE, A SOLUBLE OXYGENASE FROM TOBACCO, CATALYZES SALICYLIC-ACID BIOSYNTHESIS

Benzoic acid 2-hydroxylase (BA2H) catalyzes the biosynthesis of salicy lic acid from benzoic acid. The enzyme has been partially purified and characterized as a soluble protein of 160 kDa. High-efficiency in viv o labeling of salicylic acid with O-18(2) suggested that BA2H is an ox ygenase that specifically hydroxylates the ortho position of benzoic a cid. The enzyme was strongly induced by either tobacco mosaic virus in oculation or benzoic acid infiltration of tobacco leaves and it was in hibited by CO and other inhibitors of cytochrome P450 hydroxylases. Th e BA2H activity was immunodepleted by antibodies raised against SU2, a soluble cytochrome P450 from Streptomyces griseolus. The anti-SU2 ant ibodies immunoprecipitated a radiolabeled polypeptide of around 160 kD a from the soluble protein extracts of L-[S-35]-methionine-fed tobacco leaves. Purified BA2H showed CO-difference spectra with a maximum at 457 nm. These data suggest that BA2H belongs to a novel class of solub le, high molecular weight cytochrome P450 enzymes.