L-erythro-7,8-dihydrobiopterin(out) + a dicarboxylate(in) = L-erythro-7,8-dihydrobiopterin(in) + a dicarboxylate(out)
l-erythro-7,8-dihydrobiopterin(out) + a dicarboxylate(in) = l-erythro-7,8-dihydrobiopterin(in) + a dicarboxylate(out)