Three polypeptides with distinct biochemical properties are major alpha chain-size components of type IV collagen in...

Studies of intact type IV collagen from deposits of cultured cells or from tissues in culture, or more recently, isolated from EHS tumor have suggested that type IV collagen molecule is composed of two procollagen-like polypeptides (M(r) = 185k and 170k). We show that the major components of intact type IV collagen in bovine lens capsule are three polypeptides, two with sizes (M(r) = 180k and 175k) comparable to those of the procollagen-like polypeptides and one with a smaller size (M(r) = 160k). Both CNBr peptide mapping and electrophoretic analysis by utilizing a gel containing urea showed that the 180k polypeptide and the 160k polypeptide are chemically and genetically very similar to each other, but that the 175k polypeptide is chemically distinct from the other two polypeptides. It is unlikely that the 160k polypeptide resulted from cleavage of the 180k polypeptide during experimental manipulation, since a change of the acidic pH of extraction buffer to neutral pH, storage of the acid extract in acid for a prolonged time or incubation of the acid extract at 80 degrees C after neutralization gave rise to essentially no change in relative amount or size of the three polypeptides.