Buoyant and potentiometric titrations of synthetic polypeptides. I. Six ionizable homopolypeptides in CsCl solutions
✍ Scribed by Robert Almassy; John S. V. Zil; Lawrence G. Lum; James B. Ifft
- Publisher
- Wiley (John Wiley & Sons)
- Year
- 1973
- Tongue
- English
- Weight
- 951 KB
- Volume
- 12
- Category
- Article
- ISSN
- 0006-3525
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✦ Synopsis
Abstract
The buoyant density and potentiometric titrations of six ionizable homopolypeptides in concentrated CsCI solutions have been studied. These six homopolypeptides were chosen as models of the behavior of ionizable residues in proteins. Their buoyant and potentiometric results will be of value in interpreting the buoyant and potentiometric results observed for proteins.
The buoyant densities for all six homopolypeptides were found to increase sigmoidally as the pH is increased. These density changes are interpreted in terms of changes in the hydrations and ion binding which are associated with the titration of the residues. Preferential hydrations for the homopolypeptides are calculated. The buoyant density titrations are combined with the potentiometric titrations to determine the relationship between the buoyant density and the degree of ionization.
A better method of computing buoyant densities of proteins is described. The slope of β(ρ) has been computed for CsCl using least‐squares curve fitting and this is used in calculating the isoconcentration position. This method has been found to be more accurate than calculating the isoconcentration position from the normalized isoconcentration ratio, which is known only under limited conditions.