ζ-Carotene isomerase (EC 5.2.1.12, Z-ISO, 15-cis-zeta-carotene isomerase) is an enzyme with systematic name 9,15,9'-tricis-zeta-carotene cis-trans-isomerase. This enzyme catalyses the following chemical reaction 9,15,9'-tricis-zeta-carotene 9,9'-dicis-zeta-carotene This enzyme is involved in carotenoid biosynthesis.