<p>Members of this family are encoded by slr1293, a carotenoid biosynthesis protein which was shown to be the C-3',4' desaturase (CrtD) of myxoxanthophyll biosynthesis in <taxon tax_id="1148">Synechocystis sp.</taxon> (strain PCC 6803), and close homologues (presumed to be functionally equivalent) from other cyanobacteria, where myxoxanthophyll biosynthesis is either known or expected. This enzyme can act on neurosporene and so presumably catalyses the first step that is committed to myxoxanthophyll.</p>