citrate(out) + H(+)(out) => citrate(in) + H(+)(in)
citrate(out) + h(+)(out) => citrate(in) + h(+)(in)
citrate(out) + H(+)(out) => citrate(in) + H(+)(in)
citrate(out) + h(+)(out) => citrate(in) + h(+)(in)