The molecular parameters of monomeric and acid‐soluble collagens. Low shear gradient viscosity and electric birefringence

The molecular parameters of pronase‐treated acid‐soluble bovine skin collagen (P‐ASC) were determined from low‐shear gradient viscosity, electric birefringence, and electron microscopic data in order to determine the shear gradient range in which viscosity studies yield data which can be correctly interpreted by use of the various hydrodynamic equations for prolate ellipsoids of revolution. The P‐ASC solutions could be characterized by a single relaxation process in electric briefringence with rotary diffusion coefficient θ of 810 sec⁻¹ and a corresponding molecular length of 2850 Å. Viscosity data were found to be shear gradient dependent and only the extrapolated zero‐shear value [η]D = 0 could be used with the viscosity hydrodynamic equations to provide a correct value of molecular length. Intrinsic viscosities obtained at shear gradients >250 sec⁻¹ are nearly 30% lower than the zero‐shear value. Untreated acid‐soluble collagen (ASC) solutions contain aggregates and these appear, from electric birefringence data, to be of endlinked character. ASC solutions show a much more marked shear gradient dependence than P‐ASC. For example, at D∼500sec⁻¹,[η] = 22 dl/g, whereas the extrapolated zero‐shear value of[η] was found to be 44 dl/g. Thus, the shear gradient dependence of native collagen solutions is much more marked than previously assumed and, in contrast to the usual practice, only viscosities measured near zero shear can be interpreted in terms of molecular parameters for collagen solutions containing aggregates.