In enzymology, a putrescine N-methyltransferase (EC 2.1.1.53) is an enzyme that catalyzes the chemical reaction

S-adenosyl-L-methionine + putrescine ${\displaystyle \rightleftharpoons }$ S-adenosyl-L-homocysteine + N-methylputrescine

Thus, the two substrates of this enzyme are S-adenosyl methionine and putrescine, whereas its two products are S-adenosylhomocysteine and N-methylputrescine.

This enzyme belongs to the family of transferases, specifically those transferring one-carbon group methyltransferases. The systematic name of this enzyme class is S-adenosyl-L-methionine:putrescine N-methyltransferase. This enzyme is also called putrescine methyltransferase. This enzyme participates in alkaloid biosynthesis ii.

This enzyme is important in the synthesis of many plant alkaloids.^[1] It evolved from spermidine synthase.^[2]

• Mizusaki S, Tanabe Y, Noguchi M, Tamaki E (1971). "Phytochemical studies on tobacco alkaloids. XIV. The occurrence and properties of putrescine N-methyltransferase in tobacco roots". Plant Cell Physiol. 12: 633–640.