preferred_name: xanthine(out) + H(+)(out) => xanthine(in) + H(+)(in)
preferred_name_lc: xanthine(out) + h(+)(out) => xanthine(in) + h(+)(in)
label: xanthine(out) + H(+)(out) => xanthine(in) + H(+)(in)
label_lc: xanthine(out) + h(+)(out) => xanthine(in) + h(+)(in)