CYP83B1 is the oxime-metabolizing enzyme in the glucosinolate pathway in Arabidopsis

CYP83B1 from Arabidopsis thaliana has been identified as the oxime-metaboli zing enzyme in the biosynthetic pathway of glucosinolates. Biosynthetically active microsomes isolated from Sinapis alba converted p-hydroxyphenylacet aldoxime and cysteine into S-alkylated p-hydroxyphenylacetothiohydroximate, S-(p-hydroxyphenylacetohydroximoyl)-L-cysteine, the next proposed intermed iate in the glucosinolate pathway. The production was shown to be dependent on a cytochrome P450 monooxygenase. We searched the genome of A. thaliana for homologues of CYP71E1 (P450ox), the only known oxime-metabolizing enzym e in the biosynthetic pathway of the evolutionarily related cyanogenic gluc osides, By a combined use of bioinformatics, published expression data, and knock-out phenotypes, we identified the cytochrome P450 CYP83B1 as the oxi me-metabolizing enzyme in the glucosinolate pathway as evidenced by charact erization of the recombinant protein expressed in Escherichia coli, The dat a are consistent with the hypothesis that the oxime-metabolizing enzyme in the cyanogenic pathway (P450ox) was mutated into a "P450mox" that converted oximes into toxic compounds that the plant detoxified into glucosinolates.