Heterologous expression, purification, and enzymatic characterization of the acyclic carotenoid 1,2-hydratase from Rubrivivax gelatinosus

The carotenoid 1,2-hydratase CrtC from Rubrivivax gelatinosus has been expressed in Escherichia coli in an active form and purified by affinity chromatography. The enzyme catalyzes the conversion of various acyclic carotenes including 1-hydroxy derivatives. This broad substrate specificity reflects the participation of CrtC in 1′-HO-spheroidene and in spirilloxanthin biosynthesis. Enzyme kinetic studies including the determination of substrate specificity constants indicate that among the alternative biosynthetic routes to 1′-HO-spheroidene the one via spheroidene is the dominating pathway. In contrast to CrtC from Rvi. gelatinosus, the equivalent enzyme from Rhodobacter capsulatus, a closely related bacterium which lacks the biosynthetic branch to spirilloxanthin and accumulates spheroidene instead of substantial amounts of 1′-HO-spheroidene, is extremely poor in converting 1-HO-carotenoids. The individual catalytic properties of both carotenoid 1,2-hydratases reflect the in situ carotenogenic pathways in both purple photosynthetic bacteria.