title: Evaluation of diffusion coefficients by means of an approximate steady-state condition in sedimentation velocity distributions.
abstract: This investigation examined the feasibility of manipulating the rotor speed in sedimentation velocity experiments to spontaneously generate an approximate steady-state condition where the extent of diffusional spreading is matched exactly by the boundary sharpening arising from negative s-c dependence. Simulated sedimentation velocity distributions based on the sedimentation characteristics for a purified mucin preparation were used to illustrate a simple procedure for determining the diffusion coefficient from such steady-state distributions in situations where the concentration dependence of the sedimentation coefficient, s = s(0)/(1 + Kc), was quantified in terms of the limiting sedimentation coefficient as c → 0 (s(0)) and the concentration coefficient (K). Those simulations established that spontaneous generation of the approximate steady state could well be a feature of sedimentation velocity distributions for many unstructured polymer systems because the requirement that Kcoω(2)s(0)/D be between 46 and 183 cm(-2) is not unduly restrictive. Although spontaneous generation of the approximate steady state is also a theoretical prediction for structured macromolecular solutes exhibiting linear concentration dependence of the sedimentation coefficient, s = s(0)(1 - kc), the required value of k is far too large for any practical advantage to be taken of this approach with globular proteins.
authors: National Center for Macromolecular Hydrodynamics, School of Biosciences, University of Nottingham, Sutton Bonington Campus, Loughborough LE12 5RD, UK; Spallation Neutron and Muon Source and Research Complex at Harwell, Rutherford Appleton Laboratory, Oxfordshire OX11 0FA, UK. Electronic address: david.scott@nottingham.ac.uk.
authors: David J
authors: DJ
authors: Scott
authors: National Center for Macromolecular Hydrodynamics, School of Biosciences, University of Nottingham, Sutton Bonington Campus, Loughborough LE12 5RD, UK.
authors: Stephen E
authors: SE
authors: Harding
authors: School of Chemistry and Molecular Biosciences, University of Queensland, Brisbane, Queensland 4072, Australia.
authors: Donald J
authors: DJ
authors: Winzor
mesh_terms: D000465:Algorithms; D003198:Computer Simulation; D004058:Diffusion; D005240:Feasibility Studies; D005260:Female; D006801:Humans; D008958:Models, Molecular; D008970:Molecular Weight; D009077:Mucins / Q000032:analysis / Q000737:chemistry*; D010446:Peptide Fragments / Q000032:analysis / Q000737:chemistry*; D014461:Ultracentrifugation
chemical_list: D009077:Mucins; D010446:Peptide Fragments
keywords: Diffusion coefficient; Sedimentation velocity; Ultracentrifugation