Phytochemical studies on tobacco alkaloids XIV. The occurrence and properties of putrescine <italic>N</italic>-methyltransferase in tobacco roots

Putrescine N-methyltransferase, a new enzyme catalyzing the formation of N-methylputrescine from putrescine and S-adenosyl-L-methionine was found in roots of tobacco plants. The enzyme was purified 30-fold from crude extracts of tobacco roots. NMethylputrescine was identified as the reaction product by comparison with the authentic compound. The enzyme had a pH optimum between pH 8 and 9, and a molecular weight of about 60,000, as determined by gel filtration. Km values for putrescine and 5-adenosyl-L-methionine were 4.0 × 10−4 M and 1.1 × 10−4 M, respectively. Enzyme activity was inhibited by N-chloromercuribenzoate and Ag+. No cofactors were required. Of the various substrates tested, only putrescine served as a methyl acceptor. The enzyme was localized exclusively in the roots and its activity was gready enhanced by decapitation. The presence of putrescine N-methyltransferase in tobacco roots strongly suggests that N-methylputrescine participates as an intermediate in nicotine biosynthesis.