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, laminin1, 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 2 M
guanidine-HCl and 50 mM
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 2 M
guanidine-HCl 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 150 mM NaCl and 20 mM
phosphate, pH 7.3, at 28 degrees C contracted to 20% of the original volume on centrifugation of 1,800 x g for 10 min, while the gel formed at 4 degrees 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 important factor influencing the mechanical properties of
type IV collagen gel. The gel formed at 150 mM showed maximal rigidity in the range of 0 to 300 mM 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 degrees C in 20 mM
phosphate, pH 7.3, containing 150 mM 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.