. "\"A collagen heterotrimer containing type IV alpha chains; [alpha1(IV)]2alpha2(IV) trimers are commonly observed, although more type IV alpha chains exist and may be present in type IV trimers; type IV collagen triple helices associate to form nets within basement membranes.\" [ISBN:0721639976]" . . "collagen type IV" . "Wikipedia:Collagen_type_IV" . .