Glomerular basement membrane: evidence for collagenous domain of the alpha 3 and alpha 4 chains of collagen IV. 
A collagenous component(s) of Mr = 60K was extracted from glomerular basement membrane with urea and was purified.  Upon digestion, it yielded a collagenase-resistant fragment(s) of Mr = 23.5K. Both component and fragment showed immunochemical identity with the noncollagenous domains of the new alpha 3 & alpha 4 chains of collagen IV.  The component is characterized by a collagenous domain of about 280 residues and a noncollagenous domain of about 250 residues.  These findings further establish these new chains as distinct entities of collagen IV.