SynopsisThe angular distribution of scattered intensity and decay times of concentration fluctuations have been measured by means of digital photon counting and single-clipped photon correlation for solutions of Group C meningococcal polysaccharides at 31 "C.The z-average diffusion coefficient (D), and its second moment (D), have been determined from the time-dependent correlation function using the cumulant expansion technique. Very low observed values of (D)l and the tremendous width of the polydispersity index, which is the z-average normalized variance, suggest a higher degree of aggregation than the monomer-ctimer type self-association a t finite concentrations.
SynopsisWe report measurements of the diffusion coefficient of p-lactoglobulin A (BLG-A) a t pH = 5.60 and 4.58 in 0.10 ionic strength acetate buffer by the techniques of analog photocurrent signal correlation and digital single-clipped photon correlation. At a concentration of 21 mg/ml and a pH of 4.58, the self-association of 0-lactoglobulin can be represented by a simple dimer-octamer equilibrium model. We determined the translational diffusion coefficient of the dimer and that of the octamer using the scattering results of Kumosinski and Timasheff in a dimer-octamer mixture. Our analysis shows that the dimer OLG-A does not change its size if the pH is varied from 5.60 to 4.58 and both species remain constant in size for temperature changes from 3.5" to 25°C Hydrodynamically, the octamers behave like closed-packed spheres with an effective radius of about 45 A according to the Stokes-Einstein relation.
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