The structure of collagen

Abstract

The term collagen as at present understood embraces large numbers of fibrous proteins of animal origin which occur in widely different phyla. Although Braconnot discovered glycine in a gelatine hydrolysate in 1820, the comparative biochemistry of collagens of differing origin is still largely unknown. The physical and other chemical properties of collagen proteins, however, place them in a quite distinct group. At room temperature mammalian collagen in fibre form is inextensible beyond the rough limit associated with Hooke’s law;* it is insoluble in water, dilute acids and alkalis, and resists digestion by certain proteolytic enzymes. Collagen proteins swell characteristically in acids and alkalis, and the fibres are strongly birefringent (positive and uniaxial). The fibres also have a characteristic shrinkage temperature in hot water and other media, the exact value of which depends on the origin of the fibres. The fibrogenesis of collagen proteins is insufficiently understood, but white connective tissue fibres are usually regarded as being extracellular in origin, although there is at present no strict proof of this. Electron microscope studies of embryonic connective tissues have been made in this laboratory, and observations of fibrogenesis in tissue culture are in progress.