Computer stimulation of sedimentation in the ultracentrifuge. VII. Solutes undergoing indefinite self-association

The velocity sedimentation of solutes involved in self-association equilibria of the indefinite type was simulated using a computer model. The changes in boundary shape that resulted from varying the association constant and the molecular weight of the self-associating monomer were examined. Both ideally and nonideally sedimenting solutes were considered, and several alternative treatments of the variation of the frictional ratio with molecular size were used. All of the calculated boundaries were skewed, with the leading limb of the gradient profile steeper than the trailing limb. For relatively tightly self-associating solutes, the boundaries were very broad and strongly skewed. No shoulders or subsidiary peaks were observed for any of the model solutes used.