The Structure of Acid-soluble Basement Membrane Collagen from Bovine Anterior Lens Capsule: Molecular Parameters and Thermal Gelation Properties

Basement membrane collagen was extracted from bovine anterior lens capsules with acetic acid in the presence of protease and proteinase inhibitors. This undegraded soluble basement membrane has a sedimentation coefficient S⁰_20,W = 7.8 × 10^-13 sec^-1, a diffusion coefficient D⁰_20,w = 5.82 × 10^-8 cm²/sec and a zero-shear intrinsic viscosity [***1)] = 2200 cm³/g. These data lead to a molecular weight, M_r of 1.1 × 10⁶. Electron microscopic observation indicates that the molecules are rod-like in character with a length of 300 nm. Theoretical models describing the intrinsic viscosity in terms of the distribution of mass in such an elongated molecule show that a dumbbell-like structure is the only tenable model. In this model a single 300 nm rod-like region joins two more densely packed globular regions. The globular domains contain hydroxyproline and may have collagenase sensitive regions since digestion with purified bacterial collagenase at 37°C for 18 h degrades these domains as well as the central triple-helical domain. The intact acid-soluble basement membrane collagen precipitates from neutral pH solutions upon warming 4°C stable solutions. The pH, ionic strength and concentration dependence parameters of this thermal precipitation have been examined. The basement membrane collagen precipitation appears to be dominated by endregion domain hydrophobic interactions. The end-regions are required for precipitation in contrast to the Type I pro collagen situation wherein the intact end-regions inhibit thermal gelation. Electron microscopic examination of the basement membrane thermal gels shows networks of very thin filaments which may be related directly to the structure within intact basement membrane.