The molecular heterogeneity and diversity of reptilian keratins

Reptile keratins produce complex electrophoretic patterns, contain a number of size classes, and contain protein fractions analogous to the fractions found in other keratins. Thus, reptile keratins are similar to the heterogenous keratins of birds and mammals, and quite different from amphibian epidermal keratins. This heterogeneity may be related to the multiple functions performed by the epidermis of these organisms. The chemical diversity of reptile keratins seems to depend on the morphological differences between the tissues in which they occur. This situation is also found among these proteins in mammals and birds suggesting that keratin diversity is related to the morphological and presumably functional differentiation of epidermal tissues. The distribution of the keratin fractions in each tissue contributes to this diversity but the significance of these fractional differences is uncertain. A comparison of the half-cystine and glycine content of vertebrate alpha and ø keratins suggests that the alpha and ø proteins of reptiles may be related to the soft alpha keratins of mammals and amphibians. Mammalian hard keratins probably represent a uniquely derived group of proteins which are unlike the other vertebrate keratins. The presence of a "high sulphur" matrix component in both hard mammalian alpha and reptilian ø keratins may represent some form of molecular convergence which provides these distantly related proteins with similar physical or organizational properties.