emodin + S-adenosyl-L-methionine = questin + S-adenosyl-L-homocysteine + H(+)
emodin + s-adenosyl-l-methionine = questin + s-adenosyl-l-homocysteine + h(+)
"emodin O-methyltransferase"
"emodin o-methyltransferase"