THE COMBINATION OF CERTAIN PROTEINS WITH HYDROCHLORIC ACID

Electromotive force measurements of cells without liquid junction, of the type Ag, AgCl, HCl + protein, H2, have been made at 30°C. with the proteins gelatin, edestin, and casein in 0.1 M hydrochloric acid. The data are consistent with the assumptions of a constant combining capacity of each protein for hydrogen ion, no combination with chloride ion, and Failey's principle of a linear variation of the logarithm of the mean activity coefficient of the acid with increasing protein concentration. The combining capacities for hydrogen ion so obtained are 13.4 x 10–4 for edestin, 9.6 x 10–4 for gelatin, and 8.0 x 10–4 for casein, in equivalents of combined H+ per gm. of protein

PROTEIN FILMS ON COLLODION MEMBRANES

1. Collodion membranes of high permeability were found to adsorb weighable amounts of gelatin and egg albumin from solution at 37°C. 2. The effect of protein concentration could be expressed fairly well by a hyperbolic equation proposed by Langmuir for the adsorption of gases by a plane surface, while the usual parabolic adsorption equation of Freundlich did not fit the results. 3. In comparing this effect with solutions of varying pH, it was found there was a decided maximum of adsorption in solutions of isoelectric protein. The effects of acids and salts on the amount of gelatin adsorbed were like those observed by Loeb on the viscosity of gelatin solutions, but opposite in direction. The effects of pH on the amount of adsorbed gelatin and on the fluidity of the gelatin solutions were nearly parallel. 4. Membranes made impermeable by long drying took up very little or no gelatin from solution. 5. In the case of membranes of varying permeability the maximum amount of adherent gelatin increased with the permeability and thickness of the membranes, and appeared to be, within limits, a linear function of the relative pore surface of the membranes as calculated from Poiseuille's law. 6. The film of gelatin greatly decreased the permeability of the membranes, as measured by the flow of water through them. The relative cross-section of the pore openings, as calculated from the permeability measurements, was a linear function of the amount of adherent gelatin. These results led to the conclusion that the gelatin formed a film inside the pores

THE COMBINATION OF A STANDARD GELATIN PREPARATION WITH HYDROCHLORIC ACID AND WITH SODIUM HYDROXIDE

It has been found possible to obtain constant dry weights of sheet gelatin only by drying in vacuo at temperatures below 100°C. for a period of several weeks. Values are given for the ash and nitrogen content, the specific conductivity, and the isoelectric point of a standard gelatin preparation. By the method of E.M.F. measurements of cells without liquid junction, of the type Ag, AgCl, HCl + gelatin, H2, it has been found that this gelatin in 0.1 M HCl combines with a maximum of 9.58 x 10–4 equivalents of H+ and 2.0 x 10–4 equivalents of Cl-. By means of pH measurements with the hydrogen electrode and a KCl junction, the combination curve of this gelatin with H+ from HCl and OH- from NaOH has been determined between pH 1.1 and 12.5

MEMBRANE POTENTIALS IN THE DONNAN EQUILIBRIUM. II

Measurements were made of electromotive force in the Donnan equilibrium of systems containing dilute solutions of protein and acid. Removal of the membrane produced a decrease of no more than 2 to 4 mv. in electromotive force, while the membrane potentials, as estimated by the usual arbitrary assumption, were of the order of 12 to 34 mv. Ion ratios, as calculated from analyses for total chloride, were definitely greater than those calculated from the electromotive force of cells with salt bridges, as if there had been combination of some of the chloride ion with protein

SOME CONSEQUENCES OF THE THEORY OF MEMBRANE EQUILIBRIA

In applying Donnan's theory of membrane equilibria to systems where the non-diffusible ion is furnished by a weak acid, base, or ampholyte, certain new relations have been derived. Equations have been deduced which give the ion ratio and the apparent osmotic pressure as functions of the concentration and ionization constant of the weak electrolyte, and of the hydrogen ion concentration in its solution. The conditions for maximum values of these two properties have been formulated. It is pointed out that the progressive addition of acid to a system containing a non-diffusible weak base should not cause the value of the membrane potential to rise, pass through a maximum, and fall, but should only cause it to diminish. It is shown that the theory predicts slight differences in the effect of salts on the ion ratio in such systems, the effect increasing with the valence of the cation

THE ISOELECTRIC POINT OF GELATIN AT 40°C

Measurements have been made at 40°C. of the osmotic pressure and viscosity of 1 per cent gelatin solutions containing varying amounts of hydrochloric acid or sodium hydroxide. Each property was found to exhibit a decided minimum near pH 4.7. In the osmotic pressure experiments the pH of the inside solutions was greater than that of the outside solutions at pH values below 4.7, while it was less than that of the outside solutions at values above pH 4.7. These results indicate that gelatin at 40°C. retains its isoelectric point at about pH 4.7

THE COMBINATION OF GELATIN WITH HYDROCHLORIC ACID : II. NEW DETERMINATIONS OF THE ISOELECTRIC POINT AND COMBINING CAPACITY OF A PURIFIED GELATIN.

1. Cooper's gelatin purified according to Northrop and Kunitz exhibited a minimum of osmotic pressure and a maximum of opacity at pH 5.05 ±0.05. The pH of solutions of this gelatin in water was also close to this value. It is inferred that such gelatin is isoelectric at this pH and not at pH 4.70. 2. Hydrogen electrode measurements with KCl-agar junctions were made with concentrated solutions of this gelatin in HCl up to 0.1 M. The combination curve calculated from these data is quite exactly horizontal between pH 2 and 1, indicating that 1 gm. of this gelatin can combine with a maximum of 9.35 x 10–4 equivalents of H+. 3. Conductivity titrations of this gelatin with HCl gave an endpoint at 9.41 (±0.05) x 10–4 equivalents of HCl per gram gelatin. 4. E.M.F. measurements of the cell without liquid junction, Ag, AgCl, HCl + gelatin, H2, lead to the conclusion that this gelatin in 0.1 M HCl combines with a maximum of 9.4 x 10–4 equivalents of H+ and 1.7 x 10–4 equivalents of Cl- per gram gelatin