D-galactonate(in) + H(+)(in) <=> D-galactonate(out) + H(+)(out)
d-galactonate(in) + h(+)(in) <=> d-galactonate(out) + h(+)(out)
D-galactonate(in) + H(+)(in) <=> D-galactonate(out) + H(+)(out)
d-galactonate(in) + h(+)(in) <=> d-galactonate(out) + h(+)(out)