xanthogalenol + S-adenosyl-L-methionine <=> 4'-O-methylxanthohumol + S-adenosyl-L-homocysteine + H(+)
xanthogalenol + s-adenosyl-l-methionine <=> 4'-o-methylxanthohumol + s-adenosyl-l-homocysteine + h(+)