label: isorhamnetin + S-adenosyl-L-methionine = 3',4'-O-dimethylquercetin + S-adenosyl-L-homocysteine + 2 H(+)
label_lc: isorhamnetin + s-adenosyl-l-methionine = 3',4'-o-dimethylquercetin + s-adenosyl-l-homocysteine + 2 h(+)