The Proteins of the Keratin Component of Bird?s Beaks

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Abstract
Birds'' beaks have an outer shell of hard keratin which consists almost entirely of proteins which are very rich in glycine [about 30 residues/100 residues (residues %)], contain moderate levels of tyrosine and serine (each about 8 residues %) and which have relatively low contents of cystine (about 2.5 residues %), lysine, histidine, isoleucine and methionine. Major protein fractions in the S-carboxymethyl form isolated from the beaks of 6 different orders of birds have similar amino acid compositions, isoelectric points (pH 4.2-4.9) and MW (13,000-14,500). Detailed chromatographic electrophoretic and compositional studies of the proteins of kookaburra [Dacelo novaeguinae] beak reveal them to be a family of closely related proteins with only limited heterogeneity, in contrast to mammalian keratin systems. The major kookaburra beak fraction is similar in overall composition and molecular weight to fowl epidermal scale, kookaburra claw and turtle scute proteins and shows some resemblance to reptile claw protein. Beaks also contain small amounts of protein which are distinctly different from the major fraction but which resemble feather keratin proteins in composition and size. [Other birds studied include Tyto alba, Falco berigora, Cuculus pallidus, Gymnorhina tibicen and Calyptorhynchus lathama.].

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