3 POLYPEPTIDES WITH DISTINCT BIOCHEMICAL-PROPERTIES ARE MAJOR ALPHA-CHAIN-SIZE COMPONENTS OF TYPE-IV COLLAGEN IN BOVINE LENS CAPSULE

Studies of intact type IV collagen from deposits of cultured cells or from tissues in culture, or more recently, isolated from EHS tumor hav e suggested that type IV collagen molecule is composed of two procolla gen-like polypeptides (M(r) = 185k and 170k). We show that the major c omponents of intact type IV collagen in bovine lens capsule are three polypeptides, two with sizes (M(r) = 180k and 175k) comparable to thos e 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 t he 160k polypeptide are chemically and genetically very similar to eac h other, but that the 175k polypeptide is chemically distinct from the other two polypeptides. It is unlikely that the 160k polypeptide resu lted from cleavage of the 180k polypeptide during experimental manipul ation, 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 incub ation of the acid extract at 80-degrees-C after neutralization gave ri se to essentially no change in relative amount or size of the three po lypeptides.