Proteolysis of collagen.

Abstract

IT was shown by Linderstrom-Lang and co-workers1 that the tryptic hydrolysis of β-lactoglobulin involves the reversible denaturation of the protein as a preliminary stage. A consideration of known facts, together with new evidence obtained in connexion with an investigation of the mechanism of bating of skins in leather manufacture2, indicates that collagen and procollagen are also denatured by the enzyme prior to hydrolysis. Bating is a process in which skins, after liming and deliming, are treated with a proteolytic enzyme (usually trypsin) in order to produce a soft leather. The process has been shown to involve the removal of degraded collagen (a form of collagen in which the fibrillar structure has disintegrated and which has been named ‘progelatin’2) produced by the swelling action of lime, and is normally carried out at about 37° C. Temperature control is critical since little or no action takes place below 35° C., and above 40° C. rapid digestion of intact collagen occurs, leading to a loss of leather-making substance. The lower limit is explained by the fact that progelatin must be converted into gelatin before it can be hydrolysed by the enzyme. If, however, the skin is heated to 40–45° C. before adding the enzyme, bating can be carried out at a much lower temperature, for example, at 27° C. in about twice the time required at 37° C., which is in accord with the temperature coefficient of proteolytic enzymes acting on gelatin3. The higher temperature required to heat the progelatin in the absence of enzyme than in its presence is indicative of a denaturation stage which can be catalysed by the enzyme. As denaturation is believed to involve rupture of hydrogen bonds between parallel molecular chains, the enzyme functions as a hydrogen bond breaker in a similar manner to chemicals such as alkali, urea, potassium thiocyanate, etc.