Gelation of the Lens Capsule Type IV Collagen Solution at a Neutral pH

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It is known that the type IV collagen extracted from EHS tumor assembles under a physiological condition, but not in a gel form. The EHS type IV collagen requires the other basement membrane components, lamininl, heparansulfate proteoglycan, and/or nidogen for gelation. On the other hand, Muraoka et al. reported that the bovine lens capsule type IV collagen alone gelated under a unique and unexpected condition of 2M guanidine-HC1 and 50mM dithiothreitol, a condition which is thought to be dissociative for most biological macromolecules, including extracellular matrix [Muraoka, M. et al. (1996) J. Biochem. 119, 167-172]. The present report shows that the bovine lens capsule type IV collagen formed a gel under physiological conditions of pH and ionic environment, though the apparent rigidity of the gel was weaker than that of the gel formed in 2M guanidine-HCI and dithiothreitol. The rigidity depended greatly on the incubation temperature and NaCl concentration of the type IV collagen solution, as observed in terms of the contractility of gel volume under centrifugal force. The gel formed in 150mM NaCl and 20mM phosphate, pH 7.3, at 28°C contracted to 20% of the original volume on centrifugation of 1, 800×g for 10min, while the gel formed at 4°C, where type I collagen did not gelate at all, retained 90% of the original volume at the same centrifugal force. NaCl concentration was another impor-tant factor influencing the mechanical properties of type IV collagen gel. The gel formed at 150mM showed maximal rigidity in the range of 0 to 300mM in terms of the contractility on centrifugation. An image of a Pt/C replica of the gelated type IV collagen reconstituted at 4 or 28°C in 20mM phosphate, pH 7.3, containing 150mM NaCl showed fine meshworks consisting of rather homogeneous pore sizes, resembling the skeletal structure of basal lamina. Since the condition where the type IV collagen alone formed gels was physiological in terms of ionic strength and pH, the aggregate structure and gel properties might reflect the in vivo type IV collagen supramolecular structure and the property.