label: L-histidine + S-adenosyl-L-methionine <=> N(alpha)-methyl-L-histidine + S-adenosyl-L-homocysteine + H(+)
label_lc: l-histidine + s-adenosyl-l-methionine <=> n(alpha)-methyl-l-histidine + s-adenosyl-l-homocysteine + h(+)