The composition of collagen and acid-soluble collagen of bovine skin

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Abstract
Calf skin was extracted with dilute citrate buffer and the soluble collagen precipitated with NaCl. The amino acid composition of the citrate-soluble collagen as determined by the Moore and Stein (1951) technique was essentially the same as that of oxhide collagen. The citrate-soluble collagen contained less amide N, tyrosine and histidine and rather more hydroxyproline than the oxhide collagen. Its lysine, leucine, isoleucine and aspartic acid contents were also slightly lower. The values obtained for some of the amino acids in oxhide differed slightly from those reported in 1948 (Bowes and Kenten, 1948a) for the same sample. Reducing sugar and hexosamine determinations indicated that neither hide collagen nor the citrate-soluble collagen contained any appreciable amount of poly-saccharide. The ratio of hexosamine to N in the citrate extract after precipitation of the collagenous protein suggested the presence of muco-polysaccharide. Aspartic acid and alanine were detected as free terminal residues in the citrate-soluble protein. After conversion into gelatin by heating to 40[degree] a few additional terminal residues were detected. From consideration of the differences in composition between the hide collagen and the citrate-soluble protein it is suggested that the former is associated in some way with a protein constituent which is relatively rich in amide N, tyrosine, histidine and certain other amino acids, and relatively low in hydroxyproline. Other evidence for the presence of such a constituent in collagenous tissue is cited, and its possible significance with regard to the stability of collagen discussed.