TRNA (cytosine-5-)-methyltransferase  In enzymology, a tRNA (cytosine-5-)-methyltransferase () is an enzyme that catalyzes the chemical reaction  Thus, the two substrates of this enzyme are S-adenosyl methionine and tRNA, whereas its two products are S-adenosylhomocysteine and tRNA containing 5-methylcytosine. 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:tRNA (cytosine-5-)-methyltransferase. Other names in common use include transfer ribonucleate cytosine 5-methyltransferase, and transfer RNA cytosine 5-methyltransferase.