DETERMINATION OF SEDIMENTATION COEFFICIENTS FOR SMALL PEPTIDES

Direct fitting of sedimentation velocity data with numerical solutions of the Lamm equations has been exploited to obtain sedimentation coef ficients for single solutes under conditions where solvent and solutio n plateaus are either not available or are transient, The calculated e volution was initialized with the first experimental scan and nonlinea r regression was employed to obtain best-fit values for the sedimentat ion and diffusion coefficients. General properties of the Lamm equatio ns as data analysis tools were examined. This method was applied to st udy a set of small peptides containing amphipathic heptad repeats with the general structure Ac-YS-(AKEAAKE)(n)GAR-NH2, n = 2, 3, or 4. Sedi mentation velocity analysis indicated single sedimenting species with sedimentation coefficients (s(20,w) values) of 0.37, 0.45, and 0.52 S, respectively, in good agreement with sedimentation coefficients predi cted by hydrodynamic theory. The described approach can be applied to synthetic boundary and conventional loading experiments, and can be ex tended to analyze sedimentation data for both large and small macromol ecules in order to define shape, heterogeneity, and state of associati on.