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