PEROXIDASES FROM TULIP BULBS (TULIPA-FOSTERIANA, L.) OXIDIZE XENOBIOTICS N-NITROSODIMETHYLAMINE AND N-NITROSO-N-METHYLANILINE IN-VITRO

Tulip bulbs (Tulipa fosteriana, L.) contain peroxidases catalyzing the oxidation of the xenobiotics N-nitrosodimethylamine (NDMA) and N-nitr oso-N-methylaniline (NMA). Three anionic (A(1), A(2), A(3)) and four c ationic (B, C, D, E) peroxidases were purified from this tissue, parti ally characterized and used for kinetic studies. Demethylation of NDMA and NMA producing formaldehyde is catalyzed by one anionic (A(1)) and three cationic (C, D, E) peroxidases. The oxidation of NDMA by tulip peroxidases exhibits the Michaelis-Menten kinetics. The apparent Micha elis constant and the maximal velocity values for this substrate were determined. On the other hand, non-Michaelian kinetics for the NMA oxi dation were observed with tulip peroxidases. The most abundant cationi c peroxidase (peroxidase C) was used for detailed enzymatic studies. I n addition to formation of formaldehyde, methylaniline, aniline, 4-ami nophenol and phenol were found to be metabolites formed from NMA. Phen ol was formed presumably by N-demethylation via a benzenediazonium ion , while methylaniline, aniline and 4-aminophenol were products of deni trosation of the substrate. The efficiencies of plant peroxidases to o xidize NDMA and NMA in vitro are compared with those of cytochromes P4 50 and discussed.