The zeaxanthin biosynthesis enzyme beta-carotene hydroxylase is involved in myxoxanthophyll synthesis in Synechocystis sp. PCC 6803.

Beta-carotene hydroxylase is known to be involved in zeaxanthin synthesis. Disruption of the crtR gene encoding beta-carotene hydroxylase in Synechocystis sp. PCC 6803 resulted in the absence of both zeaxanthin synthesis and myxoxanthophyll accumulation in the mutant strain. A new carotenoid was detected in this strain. Its chemical structure was close to that of myxoxanthophyll, but the hydroxyl group on the beta-ring was lacking. This compound, deoxy-myxoxanthophyll, most likely is an intermediate in the myxoxanthophyll biosynthesis pathway. Therefore, beta-carotene hydroxylase is involved not only in zeaxanthin synthesis but also in myxoxanthophyll synthesis in Synechocystis. Furthermore, myxoxanthophyll in Synechocystis was found to have a higher molecular mass than what was determined in other species. This difference is likely to be due to a difference in the sugar moiety.