Synthesis (Fig. 3). There is no clear differentiation that would explain the near-complete conversion of -carotene to zeaxanthin by -carotene hydroxylase (CrtR), the enzyme responsible for zeaxanthin biosynthesis. We suggest a putative carotene biosynthesis pathway (Fig. 3) that accommodates the distinct complement of the carotenoid biosynthesis enzymes and their end products in A. marina.Light-Ha