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

Putrescine N-methyltransferase, a new enzyme catalyzing theformation of N-methylputrescine from putrescine and S-adenosyl-L-methioninewas found in roots of tobacco plants. The enzyme was purified30-fold from crude extracts of tobacco roots. NMethylputrescinewas identified as the reaction product by comparison with theauthentic compound. The enzyme had a pH optimum between pH 8and 9, and a molecular weight of about 60,000, as determinedby gel filtration. Km values for putrescine and 5-adenosyl-L-methioninewere 4.0 x 10^–4 M and 1.1 x 10^–4 M, respectively.Enzyme activity was inhibited by N-chloromercuribenzoate andAg⁺. No cofactors were required. Of the various substrates tested,only putrescine served as a methyl acceptor. The enzyme waslocalized exclusively in the roots and its activity was greadyenhanced by decapitation. The presence of putrescine N-methyltransferase in tobacco rootsstrongly suggests that N-methylputrescine participates as anintermediate in nicotine biosynthesis. (Received March 2, 1971; )     

STUDIES ON PROTEIN METABOLISM IN HIGHER PLANTS. III. CHANGES IN THE SOLUBLE PROTEIN COMPONENTS WITH LEAF GROWTH

Water soluble protein was extracted from tobacco leaves (BrightYellow) and fractionated through chromatographic and immunochemicalprocedures. Six different UV-absorbing components, 7 antigeniccomponents, and 4 enzyme activities (phosphatase, protease,peroxidase and RNase) were detected on the Sephadex chromatogramsof leaf extracts. An UV-absorbing fraction, Fr. I-2, (immunochemicallydesignated as Pr. Imm-I) corresponded to the known "FractionI " of S. G. WILDMAN. The contents of the three antigenic components,Imm-a, Imm-b and Imm-c, having estimated molecular weights of1 to 2 10⁵, showed significant fluctuations during growthof the leaves. Peroxidase and another antigenic component (Imm-f)of smaller molecular weight showed increase with age of theleaves. Properties of the protein components thus detected wereinvestigated. (Received May 11, 1967; )     

STUDIES ON PROTEIN METABOLISM IN HIGHER PLANTS IV. CHANGES IN PROTEIN COMPONENTS IN DETACHED LEAVES OF TOBACCO

Soluble protein fractions from tobacco leaves before and aftercuring were compared. The results of Sephadex G-200 or G-75chromatography and immunological experiments showed that theamount of larger molecular weight proteins diminished or greatlydecreased and that smaller molecular weight proteins accumulatedduring 3 days at 40 and 90% humidity after excision of theleaves from the stem. Fraction I, which was the largest proteinin the leaf extract and occupied about one-half of the solubleprotein before curing, was not found in the proteins after curing.On the contrary, the proteins contained in II-4 fraction, whichwere supposed to have smaller molecular weights, increased three-foldduring the curing. The origin of the smaller proteins was discussed. (Received May 11, 1967; )