Basement membrane collagen of renal glomerulus

Abstract

Collagen has been prepared from steer glomerular basement membrane by controlled pepsin solubilization. Four collagen polypeptides of potential alpha chain size have been isolated following denaturation and reduction with mercaptoethanol. Purification was obtained through sequential chromatography by gel filtration on agarose and by ion exchange on carboxymethyl- and diethylaminoethylcellulose and confirmed by sodium dodecyl sulfate polyacrylamide gel electrophoresis. Fractions A and B resemble interstitial alpha chains in apparent molecular weight by gel filtration (93,000). Fractions C and D were released from a single high molecular weight fraction (II) by reduction with mercaptoethanol and had a larger apparent molecular weight by gel filtration (140,000). Amino acid composition of all fractions demonstrated that they are closely interrelated by generally distinctive from interstitial collagens. Cysteine was present in all fractions except Fraction A. Prior to reduction, all mercaptan groups were inaccessible to iodoacetate and p-chloromercuribenzoate but became completely titrable after treatment with mercaptoethanol. The starting material and all fractions contained large amounts of hexose. Glucose and galactose predominated; but mannose, glucosamine, and galactosamine were also present in substantial amounts. Small amounts of fucose and sialic acids were found in starting material only.