15-cis-phytoene + 2 A => all-trans-zeta-carotene + 2 AH2
15-cis-phytoene + 2 a => all-trans-zeta-carotene + 2 ah2
15-cis-phytoene + 2 A => all-trans-zeta-carotene + 2 AH2
15-cis-phytoene + 2 a => all-trans-zeta-carotene + 2 ah2