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Crystalline preparations of rat skin acid-soluble collagen are a complex of collagen and glycoprotein of noncollagenic nature. Heat denaturation of the preparation, treatment with urea and DS-Na result in decomposition of this complex. Proteins composing it differ in amino acid composition, the presence of -S-S-bonds, the amount of a carbohydrate component, electrophoretic mobility in polyacrylamide gel and solubility in acid medium. Differential salting out by various NaCl concentrations permits separating the acid-soluble collagen preparations into fractions containing and noncontaining the accompanying noncollagen component. d

Collagen, the main protein of the connective tissue, is characterized by considerable heterogeneity. More than five types of collagen molecules, or seven types of subunits coded by different structural genes are studied. Both in the age aspects and under different pathologies the ratio of collagen types in some tissues changes, new types of collagen molecules are synthetized. Collagen not peculiar to the rat skin in normal state is synthetized in the unbalanced nitrogen nutrition with addition of amino acids, such as glycin and tryptophan.

Protein differing from the normal one by the content of S-S-bonds and by the amount of the carbohydrate component was found in the acid-soluble fraction of skin collagen in rats which were fed the protein-free diet and the protein-free diet with the glycine loading for 3 and 14 days and tryptophan for 1, 2 and 3 days. The result testifies to the fact that under extremal states in the animal skin there occurs the synthesis of collagen the structure of which differs from that in the normal animal skin.