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