Comparative Studies on the Production of Collagen The Collagen Fractions of Pig Embryo Skin

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Abstract
The neutral salt-soluble collagen fraction (NSC) obtained, in diverse ways, from pig embryo skin contains globular proteins in traces and no more than 2-4% of mucoproteids (acid polysaccharide - protein complexes). Hence, the lowered content of characteristic amino acids in embryonal soluble collagen proteins cannot be caused primarily by an admixture of non-collagenous substances but is rather their own distinctive structural feature. Water, salt and salt-citrate solvents, each separately applied to embryo skin homogenates, extract a mixture of procollagonous proteins (precursors, NSC, procollagen) of different maturity grades in considerable amounts (to 50-60%). The collagen proteins in question are presumably loosely interlinked within embryonic fibrillar tissue structures and are therefore easily extractable by any of the three solvents used. Water, salt and salt-citrate insoluble tissue residues are similar in chemical composition and always have a heightened content of hydroxyproline as compared to whole skin homogenates. An alkaline solvent, when additionally applied to the salt or salt-citrate insoluble tissue residue, extracts a considerable amount (to 65%) of procollagenous proteins of different maturity grades, which are apparently more firmly bound in the outer microphase of collagen fibrils. Whether the mature and/or theoretically conceivable immature forms of collastromin are equally extracted with alkali cannot be answered for the present. The removal of alkali-soluble substances sharply heightens the hydroxyproline content in the insoluble remainder of tissue. The properties of the latter conform to purified preparations of almost mature collastromin. Along with the fractionation of collagen proteins some of the latter proved to be non-precipitable at standard conditions, being soluble in 20% NaCl or water. They probably belong to the group of collagen protein precursors, i.e. polypeptides of different polimerization and structural maturity grades.