The strength and integrity of intact soft connective tissues are related to the forces which exist between collagen fibrils and these in turn appear to depend on collagen fibril size, density and architecture en masse. The genetic type of collagen, enzymic modifications to the collagen monomer and the proteoglycan environment all affect fibril size. Current evidence suggests that the restoration of tissue continuity and the early redevelopment of tissue strength following wounding are initially achieved by the formation of a myofibroblast-reticulin network which eventually disappears as the healing wound ages. The extent of this network defines the area in which repair tissue will be laid down and the network is equipped with the sensory apparatus to monitor the physical and chemical environment where healing is taking place and thus to direct the various facets of connective tissue synthesis outlined above. The maturation of the scar connective tissue matrix and the development of attachment between new and original connective tissues are simultaneous, related but independent processes. It takes some time before the weld is achieved by the same forces that hold connective tissue fibres together in intact tissues and the myofibroblast-reticulin network is replaced.
Guinea-pig dermis was digested with pepsin and the solubilized collagen molecules separated by differential salt precipitation at pH 7.5. Differences in subunit composition and amino acid analysis were noted between type I and type I11 collagen.Incorporation of radioactive proline into the developing foetus enabled isolation of labelled type I and type I11 collagens. Comparison of the specific activity of the isolated collagen molecules showed that type 111 collagen had a high specific activity in the early stages of foetal development, which decreased dramatically during foetal development.The specific activity of pepsin-solubilized type I collagen remained fairly constant during foetal development.Work in several laboratories has shown that dermis contains two types of collagen molecules, type I with chain composition [al(I)],a, and type I11 with chain composition [al(III)I3 [l-31. Molecules containing the ~(111) chain appear to have extremely limited solubility characteristics, and so far it has only been possible to isolate the molecules from pepsin-solubilized material. Pepsin depolymerisation of insoluble dermal collagen, under conditions which maintain the helical conformation of the collagen, enables solubilisation of type I and type 111, which can then be separated by differential salt precipitation at pH 7.5. Unlike collagen molecules previously isolated from the skin of vertebrates, the type 111 collagen molecules are cross-linked by disulphide bonds [1,2]. It has been possible using pepsin depolymerisation and differential salt precipitation to show that type I11 collagen is found in several tissues in the body, notably dermis [l-31, cardiovascular system [l] and smooth muscle tumours [l]. Its function, however, is still undetermined.Structural [2] and biosynthetic studies [4] have shown that type I11 collagen is present mainly during foetal development, and it has been suggested that the appearance of type I11 collagen in embryonic chick skin is necessary for normal ectodermal development [4].Organ culture of chick skin [4] demonstrated that type I11 collagen synthesis was largely restricted to days 8 to 12 of embryonic development, and that for the remaining 8 days until birth it was largely type I Enzyme. Pepsin A (EC 3.4.23.1).Eur. J. Biochem. 55 (1975) which was synthesized. We have been concerned with an examination in vivo of the collagen species synthesized during development of the guinea-pig, and this report is concerned with the incorporation of radioactive proline into type I and type I11 collagen during foetal development. A preliminary report of this work has been presented [5]. MATERIALS AND METHODSPregnant Duncan-Hartley guinea-pigs were given intraperitoneal injections of 50 pCi ~-[~H]proline (Radiochemicals, Amersham, Bucks). 48 h later another 50 pCi ~-[~H]proline was given. The offspring of the L-[3H]proline-labelled guinea-pigs were sacrificed one week after birth. Foetal development at the time of proline injection was determined assuming a normal gestation time for the guine...
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