Meeting Abstract
Many species of fish, reptiles, and birds have carotenoid-based integumentary coloration. No vertebrate species can synthesize carotenoids de novo; they must ingest carotenoid pigments. Once ingested, some carotenoid pigments can be modified via enzyme-supported redox reactions.Such redox reactions can change the fundamental hue of carotenoids, including transformations of yellow dietary hydroxycarotenoids (e.g. lutein) to red ketocarotenoids (e.g. 3-hydroxy-echinenone).Some songbirds use dietary pigments directly. Some songbirds ketolate dietary pigments producing red ketocarotenoids, and ketolation of yellow dietary pigments is the primary source of red coloration in songbirds(Order Passeriformes).However,the site of carotenoid metabolism in red songbirds remains uncertain and contentious.Here, we studied pigment accumulation in the livers of male house finches (Haemorhous mexicanus) that were undergoing molt and hence synthesizing ketocarotenoids from dietary carotenoids.Our goal was, to describe the specific subcellular locations of carotenoids in a putative site for production of ornamental red pigments.We collected wild male house finches that were molting red,ketocarotenoid-containing feathers and analyzed the carotenoid content of cellular fractions of homogenized liver. We found the highest concentration of ketocarotenoids in the mitochondrial fraction. And further Western blot also confirmed the positive correlation between carotenoids and mitochondria. These observations are consistent with the hypothesis that carotenoid pigments are oxidized on or within hepatic mitochondria, esterified, and then transported to the cis-face of the Golgi apparatus for secretory processing.
