Partial characterization of a second basement membrane collagen in human placenta

1. Introduction Basement membranes are extracellular structures occurring in many tissues including placenta, lung and vascular system, as well as the much thicker basement membranes of the kidney glomeruli and lens capsule. report further characterization of this collagen demonstrating the presence of more than one a-chain possibly from different molecules and a similarity of its properties with the classical basement mem- branes of lens capsule and kidney glomerull. The molecular composition of the collagen in basement membrane has recently been shown to be more complex than ~ticipated. Studies on lens .capsule [1] indicated a molecule cont~~g three identical a-chains (type IV) and these conclusions were recently supported by biosynthetic and pepsin digestion studies from this group [2]. On the other hand, it was concluded [3] that basement membranes were composed of many different collagenous peptides. More recently analysis of pepsin digests of placental membrane revealed, in addition to types I and III colIagens, a new basement membrane-like collagen [4-71. The molecular chain composition of this collagen has not yet been established. Although two ‘non-identic~ chains have been characterized it is not yet clear whether they constitute one molecule, i.e. (cuBhlrA [8] or two distinct molecules, i.e. (@A)J and (c~B)s [9] in a 2: 1 ratio. Antibodies raised against this collagen confirmed its identity as a basement mem- brane-associated collagen by immunofluorescent localization, the attached trophoblasts being clearly visible along the intensely stained membrane of the placental villi