Abstract

The composition of the skin and the variations in the relative amounts of collagen and non-collagenous proteins in the skin with the type of animal, age and nutritional level are considered. The non-collagenous proteins have been divided into four fractions on the basis of solubility and ease of extraction from skin. About 30% of the non-collagenous protein is extracted by phosphate buffer at pH 9.0 and by neutral salt solutions, a further 30% by dilute alkali, pH 12.5, and the remaining 30% or so remains in association with the insoluble collagen. Ten to twenty per cent non-collagenous protein dissolves in acetic acid together with acid-soluble collagen. The non-collagenous protein extracted by phosphate buffer, dilute alkali and acetic acid have been analysed for amino acid composition and examined by ion exchange and molecular sieve chromatography and acrylamide gel electrophoresis. The protein extracted by phosphate buffer has been shown to consist primarily of plasma proteins and is considered to arise from the blood supply and no have no function specific to skin. The non-collagenous proteins extracted by acid and alkali differ in amino acid composition. Each can be separated into a major and several minor components by acrylamide gel electrophoresis but few, if any, of these appear to be common to both extracts. The major component of the alkaline extract is of high molecular weight and is closely associated with the collagen. It represents a high proportion of the total non-collagenous protein of skin. The acid-soluble fraction is also closely associated with the collagen; it contains an excess of acidic residues and is probably bound to the collagen by electrostatic forces. The results as a whole demonstrate that the matrix of skin consists of a complex system of non-fibrous proteins, some of which are difficult to remove from association with collagen and vice versa. Their possible function in the stabilisation of skin structure is examined. These findings and recent advances in our knowledge of the structure and properties of collagen are discussed in relation to leather processing.