A study of selective adsorption of Na+ and other alkali-metal ions on isolated proteins: a test of the salt-linkage hypothesis

According to the salt-linkage hypothesis (a part of the association-induction hypothesis), the binding of alkali-metal ions on isolated proteins may be low as a result of the masking of cation-binding fixed anionic groups by the formation of "salt linkages" between them and fixed cationic groups. This hypothesis has been verified in a quantitative manner by the measurement of free and adsorbed Na+ in solutions of bovine hemoglobin titrated with increasing concentration of NaOH. In addition this communication presents data indicating (1) wide variability in the extent of Na+ adsorption among different isolated proteins and even among different samples of the same protein, (2) auto-cooperativity in the pH titration and Na+ adsorption, and (3) selectivity of the liberated fixed anionic groups for different alkali-metal ions in the rank order Na greater than Li greater than K greater than Rb, Cs.

Studies on the physical state of water in living cells and model systems. IV. Freezing and thawing point depression of water by gelatin, oxygen-containing polymers and urea-denatured proteins

Using a differential scanning calorimeter, we studied the freezing and thawing behavior of solutions of six globular proteins (hemoglobin, bovine serum albumin, gamma-globulin, beta-lactoglobulin, egg albumin, and protamine sulfate); gelatin; and three synthetic polymers (polyvinylpyrrolidone (PVP), polyvinylmethylether (PVME), and poly(ethylene oxide) (PEO)]. The native globular proteins in concentrations up to 50% produced no major change of the freezing temperature of the bulk phase water, or of the shape of the freezing peaks. In contrast, the synthetic polymers caused a lowering of the freezing temperature and a widening of the freezing peaks; the peaks disappeared at the highest macromolecular concentration and exothermic peaks appeared during subsequent warming (warming exothermic peak or WEX). Gelatin behaved like the three polymers and so did the globular proteins after denaturation with urea but not after denaturation with sodium dodecyl sulfate (SDS). These different patterns of freezing and thawing of solutions of native globular proteins and of SDS-denatured globular proteins, on the one hand, and of gelatin, PVP, PVME, PEO, and urea-denatured globular proteins, on the other, parallels perfectly the different abilities of these groups of substances to reduce the solvency of the water for solutes, reported earlier. The major new conclusion from this study is that the presence of macromolecules to a concentration as high as 50% does not necessarily inhibit or even delay to any appreciable extent the freezing of the bulk phase water present. On the other hand, inhibition of ice-formation does occur in the presence of macromolecules (e.g., gelatin, PVP) that cause multilayer polarization of the bulk phase water. The findings allow new evidence to be derived that the bulk of water in living cells also exists in the state of polarized multilayers.