Basement membrane: carbohydrates and x-ray diffraction.

The demonstration that epithelial cells of mouse and rat synthesize basement membrane antigens in tissue culture has established the concept that epithelia in general synthesize basement membrane (Pierce et al., 1964; Pierce and Nakane, 1967). Epithelial basement membranes contain hydroxyproline (Mukerjee et al., 1965). In addition, these membranes contain antigens shared by collagen and other antigens distinct from those of the connective tissue. This raises important questions regarding the nature of basement membrane: Is it collagen, a mucoprotein to be distinguished from collagen, or a combination of collagen and a mucoprotein? A major obstacle in determination of the chemical composition of basement membrane has been the difficulty in obtaining it free from connective tissue contamination. Even carefully prepared glomeruli may be heavily contaminated by periglomerular fibrous tissue or by connective tissue elements at the point of entry and exit of arterioles. Thus, the presence of collagenous components in glomerular basement membrane, as determined by chemical analysis (Spiro, 1967; Kefalides and Winzler 1966; Kefalides 1968) and x-ray diflraction, may represent a contaminant and must be confirmed on material free of connective tissue. A parietal yolk sac carcinoma of the mouse has been developed which synthesizes epithelial basement membrane in vitro or in the ascites, situations free of connective tissue cells and their products. In a previous study of the chemical composition of this neoplastic basement membrane (Mukerjee et al., 1965) hydroxyproline and hydroxylysine were found in amounts comparable to those in collagen and reticulin, but glycine was present in about half the amount characteristic of collagen. It contained more neutral sugar and hexosamine than is characteristic of collagen, and a pentose believed, on the basis of chromatographic evidence, to be lyxose. Because of the limitations of the method employed for the identification of lyxose and because of the potential importance of this observation, a detailed study of the carbohydrate portion of this basement membrane was undertaken. In addition, high-angle x-ray diffrac-