Buoyant and potentiometric titrations of synthetic polypeptides. II. Five copolypeptides and two nonionizable homopolypeptides in CsCl solutions

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The buoyant titrations of poly-L-lysine and poly-L-histidine in CsCI, RbCI, CsBr, RbBr and KBr were measured. Large differences in buoyant densities measured at low pH were observed for both polymers. Densities in the alkali chloride solutions are lower than for the bromides and the buoyant density increases as the size of the cation decreases in the halide series. All buoyant densities converge to a common value for each polymer at high pH. These data are interpreted in terms of salt-pair formation at low pH and preferential hydrations were computed both for this charged species at low pH and for the neutral polymers at high pH. The resulting data were correlated with the water activity in each buoyant solution. The variation of hydration with water activity for the charged species is found to be similar to that previously reported for bovine serum mercaptalbumin while the hydrations of the neutral polymers are found to be nearly independent of water activity. Approximate observed ionization constants were determined for each polymer in four salt solutions.

Section: Introductionmentioning

confidence: 99%

“…(23) for ovalbumin. They analyzed data of BULL and BREESE (2) who performed equilibrium dialysis measurements with ovalbumin in a variety of salt solutions as a function of concentration.…”

Section: Introductionmentioning

confidence: 99%

Buoyant and potentiometric titrations of synthetic polypeptides III. Poly-l-lysine and poly-l-histidine in five salt solutions

Ifft

Pedersen

Fujita

et al. 1978

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“…[1] Po = "r + Zx~Cx + ZyrCy + /q' v I This equation has been used several times on an empirical basis (10,23) and has recently been derived rigorously using thermodynamics by SHARP et al (22). It states that the buoyant density (P0) of a protein can be expressed in terms of the weight fractions zxand z v of the bound cations and anions, the weight fraction of bound water, Yf and the partial specific volumes, ~t and ~3, of water and the protein respectively.…”

Section: +Zx+zv+ 1-i'mentioning

confidence: 99%

The partial molar volumes of six alkali halides and their ions as a function of concentration

Pedersen

Sejersen

Ifft

1977

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The application of the technique of sedimentation equilibrium in density gradients to proteins requires a knowledge of the partial molar volumes of bound ions and water. Partial molar volumes of water and six alkali halides, CsCI, CsBr, CsI, RbCI, RbBr and RbI were computed as a function of concentration throughout the entire solubility ranges. These values were apportioned into partial molar volumes of the ions according to the cubes of Pauling's ionic radii. These data are tabulated as a function of density and water activity. The partial molar volumes of all of the salts and the ions increase with increasing salt concentration. Unique triple points are observed in the plots of the partial molar volumes of both the rubidium and cesium ions as a function of density.

“…3) The value of 0.249 g/ml was calculated by SHARP et al (21) from the slope of a I~ vs degree of ionization plot. This plot was found unsatisfactory by the same authors due to scatter of the points.…”

Section: Density Gradient Experimentsmentioning

confidence: 99%

“…From the determined Oo'S it is possible to es-timate the extend of hydration or binding of anions and cations to the proteins. In order to get a better understanding of the contribution from the individual ionizable groups to hydration and ion binding, a series of experiments was initiated in which the buoyant titration curves for synthetic polypeptides (1,21) and proteins (13,20,25) were determined. The present article is a contribution to these studies.…”

Section: Introductionmentioning

confidence: 99%

Buoyant titration of bovine mercaptalbumin chemically modified at the carboxyl groups

Svendsen

1976

Bovine mercaptalbumin has been modified at the carboxyl groups by means of I-ethyl-3 (3-dimethylisopropyl) carbodiimide and glycine amide. A stable derivative was obtained after modification of 54 groups. The modified protein differed only slightly from the unmodified one with respect to the optical rotatory dispersion parameters ao, bo and ~. This preparation was studied in the analytical ultracentrifuge in a CsCI gradient in the pH-interval from 2 to 1 I. The buoyant densities were determined and compared with those of the unmodified protein in the same pH-interval. The contribution from the carboxyl groups to the buoyant density is discussed and compared with results obtained with other proteins and synthetic polypeptides.