ISOLATION AND CHARACTERIZATION OF COLLAGEN FROM GLOMERULAR BASEMENT MEMBRANE

The collagen from normal dog glomerular basement membrane was isolated after solubilization with Pronase at low temperatures. This protein, which is separated by precipitation with 15% KCl, contains in terms of residues/1000 residues: glycine, 325; hydroxyproline, 162; proline, 60; hydroxylysine, 40; lysine, 4; and half-cystine, 6. Hexose accounts for 10.4% of dry weight. There is 5.12% glucose and 5.22% galactose. On acrylamide electrophoresis at pH 4.8, the collagen resolves into three fast components, two components with slower mobility, and one with least mobility; all bands stain for protein and carbohydrate. This collagen has a sedimentation constant, s20,w, of 3.45 S and an intrinsic viscosity of 5.2 dl/g. Optical rotation and circular dichroism studies revealed a triple-helical structure. The molecular weight is approximately 210,000. Reconstitution of the soluble collagen by precipitation with adenosine triphosphate reveals fibers of variable dimensions. Material obtained by treatment with Pronase at 4° for 24 hr gave SLS-type aggregates measuring about 1660 and 3250 Å, the latter being aggregates of the former. The data show that basement membrane collagen is a unique mammalian protein rich in hydroxylysine, hydroxyproline, and carbohydrate. Unlike other mammalian collagens its contains cystine. As it is obtained after Pronase treatment of basement membrane, it has about two-thirds the length and molecular weight of ordinary mammalian skin collagen. The possibility that this may result from limited cleavage of the body of the collagen molecule cannot at present be excluded. It is associated with a glycoprotein which is unlike collagen. This association may be responsible for the failure of this collagen to form large aggregates in vivo and may be related to the functional requirements of glomerular basement membrane. © 1968, American Chemical Society. All rights reserved.