ELONGATIONAL FLOW STUDIES ON TYPE-IV COLLAGEN - COMPARISON WITH TYPE-I

Elongational flow techniques have been used to investigate the birefri ngent response of monodisperse type IV collagen in dilute solution and the results compared with type I collagen. A four-roll mill apparatus was used to characterize the solutions at low strain rates, epsilon l ess-than-or-equal-to 300 s-1. The birefringence is nonlocalized and ri ses gradually to a plateau value, in accordance with rigid-rod behavio r. The gradients of the tangent to the curves at zero strain rate are estimated for types IV and I collagen. The concentrations of the solut ions used were in the dilute to semidilute regimes. Using a value of 3 00 nm for the length of type I collagen, values of 364-408 nm were cal culated for the length of the type IV collagen molecule, depending on the concentration regime chosen, which is consistent with biochemical predictions based on a rigid molecule. The results imply that the beha vior of type IV collagen molecules in solution is similar to type I co llagen, despite the presence of several sequence interruptions in the type IV helix.