Experiments concerning the Effect of Enzymes on the Reconstitution of Collagenous Fibrils in Vitro

PLATE 95 Existence and nature of the cement substance which binds the collagenous fibers and fibrils have been widely discussed. I t has been shown that this material , probably mucoproteins, can be, at least partially, removed from the fibers not only by salts such as KC1 and CaC12, but also b y treating the fibers with trypsin (13). A cement substance which is probably of a nature similar to that within the microscopically visible fibers has been shown by the electron microscope to be present between the cross-banded microfibrils (Wasser-mann (13)). Considering the coexistence of mucopolysaccharides and collagenous material during fibrillogenesis, it may be asked whether or not mucopolysaccharides take part in the building and the structure of the collagenous microfibrils. This question has been raised repeatedly, and several authors using chemical and physicochemical methods came to the conclusion that a collagen-mucopolysaccharide complex does exist (Bur-ton et al. (6) suggest that "the mucopolysaccharide and protein component of the granules (of the fibroblasts) may have fibrogenic properties." On the other hand, Schmitt, Gross, and Highberger (10), considering the question "whether or not a small amount of carbohydrate material is associated with the tropocollagen in forming collagen fibers," found by their own analysis "that the most highly purified colla-gen contains only a very small carbohydrate residue," which may be only an impurity due to adhering ground substance material. The observation that trypsin seems to hydrolyze the cement substance may offer an interpretation of Sizer's statement (9) that collagen fibers are, contrary to the experience of the histologists, digestible in trypsin when cut in very small pieces, and of D. S. Jackson's suggestion (5) that chondroitin sulfuric acid may serve as "a factor in the stability" of collagenous fibers: that is, not the collagen but the mucoprotein cement substance might have been attacked by trypsin in Sizer's, or by hyaluronidase in Jackson's experiments. On the has been received. The authors found that collagen and "procollagen" undergo degradation when dissolved by periodate and phenyliodoso acetate, and concluded that "the degradation is probably based on an attack on the carbohydrate groupings present in collagen and procollagen." 299