DISTRIBUTION AND ACTIVITY OF MICROSOMAL NADPH-DEPENDENT MONOOXYGENASES AND AMINO-ACID DECARBOXYLASES IN CRUCIFEROUS AND NON-CRUCIFEROUS PLANTS, AND THEIR RELATIONSHIP TO FOLIAR GLUCOSINOLATE CONTENT

The NADPH-dependent conversion of amino acids to their aldoximes is an initial step in glucosinolate biosynthesis. A number of microsomal al doxime-forming monooxygenase activities were detected in leaves from a variety of glucosinolate-containing species, whereas barley, bean and tobacco leaves did not contain any such activities. The substrates fo r these monooxygenases in each species largely correlated with the spe ctrum of glucosinolates found in that species. No activity was detecte d that metabolized homomethionine (supposed precursor of 2-propenylglu cosinolate [sinigrin]), even in species where sinigrin was the major g lucosinolate. Zn Sinapis species containing hydroxybenzylglucosinolate (sinalbin), activity with L-Tyr was detected, whereas Brassica specie s containing sinalbin had no such activity. However, these Brassicas d id contain an L-Phe monooxygenase activity. Partial characterization o f the monooxygenases indicated that in Brassica species, Nasturtium of ficinalis and Raphanus sativus these resembled the flavin-linked monoo xygenases previously found in oilseed rape (Brassica napus) and Chines e cabbage (Brassica campestris). The L-Tyr-dependent activity in Sinap is species, and the L-Phe-dependent activity in Tropaeolum majus, had characteristics of cytochrome P450-type enzymes. No similarity was fou nd with any other known amino acid metabolizing enzymes (including dec arboxylases, amino acid oxidases and diamine/polyamine oxidases).