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Publication Abstract from PubMed

Carotenoid cleavage oxygenases (CCOs) are non-heme, Fe(II)-dependent enzymes that participate in biologically important metabolic pathways involving carotenoids, apocarotenoids including retinoids, stilbenes and related compounds. CCOs typically catalyze the cleavage of non-aromatic double bonds by dioxygen (O2) to form aldehyde or ketone products. Expressed only in vertebrates, the RPE65 sub-group of CCOs catalyzes a non-canonical reaction consisting of concerted ester cleavage and trans-cis isomerization of all-trans-retinyl esters. It remains unclear whether the former group of CCOs function as mono- or di-oxygenases. Additionally, a potential role for O2 in catalysis by the RPE65 group of CCOs has not been evaluated to date. Here, we investigated the pattern of oxygen incorporation into apocarotenoid products of Synechocystis apocarotenoid oxygenase (ACO). Reactions performed in the presence of 18O-labeled water and 18O2 revealed an unambiguous dioxygenase pattern of O2 incorporation into the reaction products. Substitution of Ala for Thr at position 136 of ACO, a site predicted to govern the mono- vs. dioxygenase tendency of CCOs, greatly reduced enzymatic activity without altering the dioxygenase labeling pattern. Reevaluation of the oxygen-labeling pattern of the resveratrol-cleaving CCO, NOV2, previously reported to be a monooxygenase, using a purified enzyme sample revealed that it too is a dioxygenase. We also demonstrated that bovine RPE65 is not dependent on O2 for its cleavage/isomerase activity. In conjunction with prior research, the results of this study resolve key issues regarding the utilization of O2 by CCOs and indicate that dioxygenase activity is a feature common amongst double bond-cleaving CCOs.

Utilization of Dioxygen by Carotenoid Cleavage Oxygenases.,Sui X, Golczak M, Zhang J, Kleinberg KA, von Lintig J, Palczewski K, Kiser PD J Biol Chem. 2015 Oct 23. pii: jbc.M115.696799. PMID:26499794^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.