(9Z,12Z)-octadecadienoyl-CoA + 2 Fe(III)-[cytochrome b5] + 2 H2O => (9Z)-octadecenoyl-CoA + 2 Fe(II)-[cytochrome b5] + O2 + 2 H(+)
(9z,12z)-octadecadienoyl-coa + 2 fe(iii)-[cytochrome b5] + 2 h2o => (9z)-octadecenoyl-coa + 2 fe(ii)-[cytochrome b5] + o2 + 2 h(+)