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Binxing Li, Jeanne M. Frederick, Paul S. Bernstein; Expression of β-Carotene 9’, 10’ Monooxygenase (BCO2) In Human Retina And RPE-Choroid. Invest. Ophthalmol. Vis. Sci. 2011;52(14):2329.
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β-Carotene 9’, 10’ monooxygenase (BCO2) specifically cleaves the 9’, 10’-double bond of β-carotene, lycopene, and possibly xanthophylls. Genetic variations in the BCO2 gene have been found to be associated with lutein accumulation in animals. Human BCO2 exists in two isoforms: one variant (V1) of 579 amino acids and the other variant (V2) of 545 amino acids. To determine whether BCO2 is present and participates in carotenoid metabolism of the primate retina, we investigated the expression of BCO2 (V1) and (V2) in human retina, RPE-choroid, and liver.
RT-PCR was used to test mRNA transcription of BCO2 in human retina, RPE-choroid and liver. Western blots and immunohistochemistry using a commercially-available antibody that can recognize both BCO2 (V1) and (V2) were used to probe the expression and distribution of BCO2 in human and monkey retina.
RT-PCR detected stronger mRNA expression of BCO2 (V1) in human retina with a 440-bp band and higher mRNA expression of BCO2 (V2) in human RPE-choroid and liver with a 170-bp band. Immunoblot results showed a 63-kDa band in human retina and a 59-kDa band in human RPE-choroid and liver, suggesting that BCO2 (V1) is expressed specifically in retina, whereas BCO2 (V2) is expressed predominantly in RPE-choroid and liver. Immunohistochemistry results revealed that BCO2 (V1) is localized broadly among neuronal cell bodies of monkey retina.
Human BCO2 (V1) is expressed specifically in human retina, while BCO2 (V2) is expressed in human RPE-choroid and liver. This specific and distinct tissue distribution of human BCO2 (V1) and (V2) indicates that they may play different roles in human ocular carotenoid metabolism. Functional studies of their enzymatic activities and specificities are in progress.
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