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ABSTRACT The carotenoid‐based colours of birds are a celebrated example of biological diversity and an important system for the study of evolution. Recently, a two‐step mechanism, with the enzymes cytochrome P450 2J19 (CYP2J19) and 3‐hydroxybutyrate dehydrogenase 1‐like (BDH1L), was described for the biosynthesis of red ketocarotenoids from yellow dietary carotenoids in the retina and plumage of birds. A common assumption has been that all birds with ketocarotenoid‐based plumage coloration used this CYP2J19/BDH1L mechanism to produce red feathers. We tested this assumption in house finches (Haemorhous mexicanus) by examining the catalytic function of the house finch homologues of these enzymes and tracking their expression in birds growing new feathers. We found that CYP2J19 and BDH1L did not catalyse the production of 3‐hydroxy‐echinenone (3‐OH‐echinenone), the primary red plumage pigment of house finches, when provided with common dietary carotenoid substrates. Moreover, gene expression analyses revealed little to no expression ofCYP2J19in liver tissue or growing feather follicles, the putative sites of pigment metabolism in moulting house finches. Finally, although the hepatic mitochondria of house finches have high concentrations of 3‐OH‐echinenone, observations using fluorescent markers suggest that both CYP2J19 and BDH1L localise to the endomembrane system rather than the mitochondria. We propose that house finches and other birds that deposit 3‐OH‐echinenone as their primary red plumage pigment use an alternative enzymatic pathway to produce their characteristic red ketocarotenoid‐based coloration.
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Substrates, intermediates, and products of avian ketocarotenoid metabolism
Carotenoid-based coloration is an essential feature of avian diversity and has important roles in communication and mate choice. The red feathers of birds from phylogenetically diverse orders and families are pigmented with C4-ketocarotenoids produced via the successive action of Cytochrome P450 2 J19 (CYP2J19) and 3-hydroxybutyrate dehydrogenase 1-like (BDH1L) on yellow dietary precursors. Yet, the biochemistry of these enzymes remains incompletely understood. Here we present a series of experiments characterizing the substrates, intermediates, and products of CYP2J19 and BDH1L expressed in heterologous cell culture. We confirm that CYP2J19 preferentially hydroxylates the 4 and 4′ positions of β-ring substrates, but can also hydroxylate the 3 and 3′ positions of C4-ketocarotenoids. We confirm that BDH1L catalyzes the conversion of zeaxanthin to canary xanthophyll B (ε,ε’-carotene-3,3′-dione) a major pigment in plumage of many yellow bird species. These results suggest that the actions of CYP2J19 and/or BDH1L can explain the presence of many metabolically transformed carotenoids in avian tissues.
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- PAR ID:
- 10610455
- Publisher / Repository:
- Elsevier
- Date Published:
- Journal Name:
- Biochimica et Biophysica Acta (BBA) - Molecular and Cell Biology of Lipids
- ISSN:
- 1388-1981
- Page Range / eLocation ID:
- 159654
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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