cytidine(50) in tRNA + S-adenosyl-L-methionine = 5-methylcytidine(50) in tRNA + S-adenosyl-L-homocysteine + H(+)
cytidine(50) in trna + s-adenosyl-l-methionine = 5-methylcytidine(50) in trna + s-adenosyl-l-homocysteine + h(+)