POLYELECTROLYTE PROPERTIES OF PROTEOGLYCAN MONOMERS

Light scattering measurements were made on proteoglycan monomers (PGM) over a wide range of ionic strengths C(s), and proteoglycan concentrations [PG]. At low C(s) there were clear peaks in the angular scattering intensity curve I(q), which moved towards higher scattering wave numbers q, as [PG]1/3. This differs from the square root dependence of scattering peaks found by neutron scattering from more concentrated polyelectrolyte solutions. The peak remained roughly fixed as C(s) increased, but diminished in height, and superposed I(q) curves yielded a sort of isosbestic point. Under certain assumptions the static structure factor S(q) could be extracted from the measured I(q), and was found to retain a peak. A simple hypothesis concerning coexisting disordered and liquidlike correlated states is presented, which qualitatively accounts for the most salient features of the peaks. There was evidence of a double component scattering autocorrelation decay at low C(s), which, when resolved into two apparent diffusion coefficients, gave the appearance of simultaneous "ordinary" and "extraordinary" phases. The extraordinary phase was "removable", however, by filtering. At higher C(s) the proteoglycans appear to behave as random nonfree draining polyelectrolyte coils, with a near constant ratio of 0.67 between hydrodynamic radius and radius of gyration. The apparent persistence length varied as roughly the - 0.50 power of ionic strength, similar to various linear synthetic and biological polyelectrolytes. Electrostatic excluded volume theory accounted well for the dependence of A2 on C(s).