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Donnan effect as measured by sedimentation equilibrium for the protein cytochrome c
Author(s) -
Syvanen Michael,
Schachman H. K.
Publication year - 1978
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.1978.360170412
Subject(s) - chemistry , sedimentation equilibrium , salt (chemistry) , dilution , activity coefficient , triethylamine , thermodynamics , cytochrome c , component (thermodynamics) , extrapolation , donnan potential , chromatography , aqueous solution , organic chemistry , ultracentrifuge , biochemistry , mitochondrion , physics , mathematical analysis , mathematics , electrode , electrolyte
The protein turkey‐heart cytochrome c is used as a model protein to study charge effects in sedimentation equilibrium experiments in three‐component solutions. Data are given for the dependence of the apparent M (1– υ ρ) on ρ in solutions of KCl, RbCl, CsCl, and triethylamine hydrochloride. The results show the Donnan effect to have a significant influence on the apparent molecular weight, found by extrapolation of the data to a solution density of one. The apparent molecular weights are for protein at infinite dilution. A theoretical treatment is presented where the magnitude of this effect can be predicted accurately from the formal net charge of the protein as computed from the amino acid composition. The results are shown to be important in computing the preferential hydration of the protein in concentrated salt solutions. For such systems the Donnan effect should be subtracted from the total interaction coefficient for multicomponent system in order to obtain the preferential hydration.