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Equilibrium sedimentation of a polyelectrolyte in a density gradient of a low‐molecular weight electrolyte. I. DNA in CsCl
Author(s) -
Daniel Ezra
Publication year - 1969
Publication title -
biopolymers
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.556
H-Index - 125
eISSN - 1097-0282
pISSN - 0006-3525
DOI - 10.1002/bip.1969.360070308
Subject(s) - chemistry , electrolyte , density gradient , sedimentation equilibrium , polyelectrolyte , counterion , sedimentation , differential centrifugation , molecule , thermodynamics , analytical chemistry (journal) , chromatography , ion , ultracentrifuge , organic chemistry , polymer , physics , biochemistry , paleontology , electrode , quantum mechanics , sediment , biology
Previous work had indicated that the molecular weight calculated from the equilibrium distribution of DNA in a CsCl density gradient appears to be one half the estimated value of the true molecular weight. In the present study, the sedimentation equilibrium of a polyclectrolyte in a density gradient generated by a low molecular weight electrolyte is treated in terms of the representation according to which a constant fraction of the counterions is considered permanently immobilized and the remaining fraction completely free. Equations for the preferential hydration and the molecular weight are obtained. The validity of the treatment is tested by applying it to experimental data on the equilibrium sedimentation of ϕX 174 DNA in CsCl, and it is found that the molecular weight calculated in this way is in agreement with the accepted value for this molecule. Also, recalculation of published data on density gradient centrifugation of T2 DNA in CsCl according to the present treatment brings up the molecular weight to within the range of values given by other methods.