Biosynthetic studies on the collagenous components of basement membranes

The biosynthesis of the collagenous components of the rat lens capsule and glomerular basement membrane (GBM) has been investigated. Intact lenses, isolated lens capsules and isolated renal glomeruli incorporate [3H]proline into 4-hydroxy[3H]proline containing polypeptides of approximate molecular weight 180,000 (analysed under reducing conditions). These polypeptides are deposited in the deoxycholate-insoluble basement membrane matrix and correspond to subunits of the intact, non-radioactive basement membranes. With time a proportion of the newly synthesised collagenous polypeptides become assembled into high molecular weight aggregates which are stabilized by lysine- and/or hydroxylysine-derived cross-links. Despite the similar patterns of collagen biosynthesis in the rat lens capsule and GMB, the latter has a more complex polypeptide composition the origin of which remains uncertain.