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Publication : Identification, expression, and substrate specificity of a mammalian beta-carotene 15,15'-dioxygenase.

First Author  Redmond TM Year  2001
Journal  J Biol Chem Volume  276
Issue  9 Pages  6560-5
PubMed ID  11092891 Mgi Jnum  J:67765
Mgi Id  MGI:1931377 Doi  10.1074/jbc.M009030200
Citation  Redmond TM, et al. (2001) Identification, expression, and substrate specificity of a mammalian beta-carotene 15,15'-dioxygenase. J Biol Chem 276(9):6560-5
abstractText  We have identified from mouse the first mammalian beta-carotene 15,15'-dioxygenase (beta-CD), a crucial enzyme in development and metabolism that governs the de novo entry of vitamin A from plant-derived precursors. beta-CD is related to the retinal pigment epithelium-expressed protein RPE65 and belongs to a diverse family that includes the plant 9-cis-epoxycarotenoid dioxygenase and bacterial lignostilbene dioxygenases. beta-CD expression in Escherichia coli cells engineered to produce beta-carotene led to the accumulation of all-trans-retinal at the expense of beta-carotene, confirming that beta-CD catalyzed the central cleavage of this vitamin A precursor. Purified recombinant beta-CD protein cleaves beta-carotene in vitro with a V(max) of 36 pmol of retinal/mg of enzyme/min and a K(m) of 6 microm. Non-provitamin A carotenoids were also cleaved, although with much lower activity. By Northern analysis, a 2.4-kilobase (kb) message was observed in liver, kidney, small intestine, and testis, tissues important in retinoid/carotenoid metabolism. This message encoded a 63-kDa cytosolic protein expressed in these tissues. A shorter transcript of 1.8 kb was found in testis and skin. Developmentally, the 2.4-kb mRNA was abundant at embryonic day 7, with lower expression at embryonic days 11, 13, and 15, suggesting a critical role for this enzyme in gastrulation. Identification of beta-CD in an accessible model organism will create new opportunities to study vitamin A metabolism.
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