title: High Concentrations of Ketocarotenoids in Hepatic Mitochondria of Haemorhous mexicanus.
abstract: Vertebrates cannot synthesize carotenoid pigments de novo, so to produce carotenoid-based coloration they must ingest carotenoids. Most songbirds that deposit red carotenoids in feathers, bills, eyes, or skin ingest only yellow or orange dietary pigments, which they oxidize to red pigments via a ketolation reaction. It has been hypothesized that carotenoid ketolation occurs in the liver of vertebrates, but this hypothesis remains to be confirmed. To better understand the role of hepatocytes in the production of ketolated carotenoids in songbirds, we measured the carotenoid content of subcellular components of hepatocytes from wild male house finches (Haemorhous mexicanus) that were molting red, ketocarotenoid-containing feathers (e.g., 3-hydroxy-echinenone). We homogenized freshly collected livers of house finches and isolated subcellular fractions, including mitochondria. We found the highest concentration of ketocarotenoids in the mitochondrial fraction. These observations are consistent with the hypothesis that carotenoid pigments are oxidized on or within hepatic mitochondria, esterified, and then transported to the Golgi apparatus for secretory processing.
authors.affiliation: Department of Biological Sciences, 331 Funchess Hall, Auburn University, Auburn, Alabama 36849-5414; 2School of Life Sciences, Arizona State University, Tempe, Arizona 85287-4501.
authors.forename: Zhiyuan
authors.initials: Z
authors.lastname: Ge
authors.forename: James D
authors.initials: JD
authors.lastname: Johnson
authors.forename: Paul A
authors.initials: PA
authors.lastname: Cobine
authors.forename: Kevin J
authors.initials: KJ
authors.lastname: McGraw
authors.forename: Rosana
authors.initials: R
authors.lastname: Garcia
authors.forename: Geoffrey E
authors.initials: GE
authors.lastname: Hill
mesh_terms: D000818:Animals; D002338:Carotenoids / Q000378:metabolism*; D005241:Feathers; D046369:Finches / Q000502:physiology*; D008099:Liver / Q000378:metabolism*; D008297:Male; D008930:Mitochondria, Liver / Q000378:metabolism; D018978:Molting; D010858:Pigmentation; D013347:Subcellular Fractions / Q000378:metabolism
chemical_list: D002338:Carotenoids