Biosynthesis
Due to the commercial value of carotenoids, their biosynthesis has been studied extensively in both natural producers, and non-natural (heterologous) systems such as the bacteria Escherichia coli and yeast Saccharomyces cerevisiae. Zeaxanthin biosynthesis proceeds from beta-carotene via the action of a single protein, known as a beta-carotene hydroxylase, that is able to add a hydroxyl group (-OH) to carbon 3 and 3' of the beta-carotene molecule. Zeaxanthin biosynthesis therefore proceeds from beta-carotene to zeaxanthin (a di-hydroxylated product) via beta-cryptoxanthin (the mono hydroxylated intermediate). Although functionally identical, several distinct beta-carotene hydroxylase proteins are known. Due to the nature of zeaxanthin, relative to astaxanthin (a carotenoid of significant commercial value) beta-carotene hydroxylase proteins have been studied extensively.
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