Szukana fraza: [Abstract = "The coloration of these feathers is due to their infusion with the pigment melanin, which birds synthesize endogenously during a series of conversion steps beginning with the enzymatic oxidation of the amino acid tyrosine. Copper is the cofactor of the enzyme responsible for this process, and it is possible that copper level limits the activity of the enzyme and therefore limits melanin production. We tested this hypothesis by manipulating the level of dietary copper available to individually caged juvenile and adult house sparrows \(\?Passer domesticus\?\) throughout their moult."]

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