title: Hidden self-association of proteins.
abstract: Sedimentation equilibrium measurements were carried out on solutions of bovine serum albumin, aldolase, and ovalbumin in phosphate-buffered saline, pH 7.2, at 10 degrees C. The data obtained for each protein were analyzed to yield the dependence of apparent weight-average molecular weight upon protein concentration, over a concentration range of ca 1-200 g/L. Using the approximate theory of Chatelier and Minton [1987) Biopolymers 26, 507-524), models are formulated for the dependence of apparent weight-average molecular weight upon concentration in non-ideal solutions containing proteins which may self-associate according to a monomer/n-mer or a monomer/dimer/tetramer scheme. The concentration dependence data for serum albumin may be accounted for, assuming either no self-association or weak monomer/dimer association. The data for aldolase may be accounted for assuming either weak monomer/dimer or weak monomer/trimer association. The data for ovalbumin may be accounted for assuming either weak monomer/trimer or weak monomer/dimer/tetramer association. The associations do not approach saturation at the highest concentrations studied, and the standard-state free energy changes accompanying self-association amount to less than 4 kcal/mol of intermolecular contacts, suggesting that non-specific clustering of protein molecules at high concentration rather than the formation of specific complexes is being observed.
authors.affiliation: Section on Pharmacology, National Institute of Diabetes and Digestive and Kidney Diseases, Bethesda, Maryland 20892.
authors.forename: N
authors.initials: N
authors.lastname: Muramatsu
authors.forename: A P
authors.initials: AP
authors.lastname: Minton
mesh_terms: D000818:Animals; D002417:Cattle; D005634:Fructose-Bisphosphate Aldolase; D008954:Models, Biological; D008970:Molecular Weight; D010047:Ovalbumin; D011506:Proteins; D011817:Rabbits; D012710:Serum Albumin, Bovine; D013816:Thermodynamics
chemical_list: D011506:Proteins; D012710:Serum Albumin, Bovine; D010047:Ovalbumin; D005634:Fructose-Bisphosphate Aldolase