Ion-exchange displacement chromatography of proteins, using narrow-range carboxymethyldextrans and a new index of affinity.

A new method of characterizing carboxymethyldextrans with respect to their relative affinities for an anion exchanger can be applied not only to pure preparations but also to fractions of a displacement chromatogram in which these polyanions have been used as spacers. This, along with the development of a means of preparing carboxymethyldextrans with narrow ranges of affinity, as contrasted with the very heterogeneous preparations previously used, has greatly facilitated the focusing of resolving power on critical regions of the chromatogram. The effectiveness of this approach is illustrated by the separation of proteins that differ only slightly in affinity, using the genetic variants of beta-lactoglobulin as one model and the numerous components of purified ovalbumin as another.