Edward S. DellaMonica

Binding of calcium to casein: Influence of pH and calcium and phosphate concentrations

Abstract The binding of calcium to casein has been determined, both by analysis of the aggregated casein and by equilibrium dialysis. Values for maximum amount of calcium bound and dissociation pK values are reported for pH 7.0 and compared with values in the literature. Calcium is not bound to casein at pH 5, but binding does occur and increases as the pH is raised. The increase in binding parallels the increase in net negative charge of the casein, as well as the degree of ionization of a substituted phosphoric acid up to about pH 7. The time that the calcium caseinate aggregates are permitted to form does not affect the calcium binding. Aggregates formed at higher temperature in part redissolve at lower temperatures, but the binding of calcium per unit weight of aggregate is unchanged. In casein systems containing both calcium and phosphate, binding of the latter occurs only above pH 6, and simultaneously the binding of calcium increases greatly. The isoelectric point (maximum precipitation) of casein is not changed in the presence of calcium chloride.

Purification of human red cell acetylcholinesterase

Abstract The acetylcholinesterase in human red blood cells was extracted from the stromata by means of the surface-active substance polyoxyethylene sorbitan monolaurate (Tween 20). After a series of purification steps, preparations dried in the frozen state were freed of Tween by extraction with acetone and freed of lipide by extraction with n-butanol or ethanol. The dry powders, representing a 250-fold purification, were stable at 7 °. Electrophoresis on paper showed that the isoelectric point of the esterase lies below pH 6.0.

Use of butanol in the purification of the alkaline phosphatase of bovine milk

Summary The alkaline phosphatase of bovine milk has been purified more than 1000-fold by dissociation of the phosphatase complex with n -butanol and subsequent fractionation with acetone. This extends the usefulness of the n -butanol treatment originally used for the purification of the alkaline phosphatase in cream.

Separation of proteins by gradient solvent extraction of a protein precipitate

Abstract A mixture of bovine serum albumin and human hemoglobin is used to show the applicability of the gradient extraction method for the fractionation of proteins. The mixture is precipitated with ammonium sulfate and serially extracted with ammonium sulfate solution continuously diluted with water. The method has also revealed a reduction in the solubility of α-lactalbumin that had been dried from the frozen state and stored at 25 °. Equipment for accomplishing the continuous dilution is described as well as calculations of the concentrations to be expected.

Determination of partition coefficients by headspace gas chromatography

Abstract Air-water partition coefficients of ethylacetate are determined by analysis of the headspace vapor from a closed system containing ethyl acetate and sodium chloride solutions of various concentrations. Knowing the amount of ethyl acetate in the headspace, it is possible to calculate the partition coefficient. This paper describes a simple method of determining these values without gas injection valves or other specialized equipment. The values obtained are within 7% of previously published values.

Purification of human red cell acetylcholinesterase by electrophoresis, ultracentrifugation and gradient extraction

Abstract Purification of human red cell cholinesterase by means of electrophoresis on paper, ultracentrifugation, and gradient exctraction is described. By these means a protein is isolated that appears to be homogeneous in gradient extraction and free electrophoresis; however, reasons are given for believing that this is not the cholinesterase protein but a major protein with which the cholinesterase is tenaciously associated.

Casein and paracasein: Neutralization with alkali, precipitation by calcium chloride and binding of calcium

Abstract The amount of NaOH required to neutralize casein and paracasein was found to be essentially equal, namely 60–64 × 10−5 moles/g. At the same concentration of CaCl2, almost equivalent amounts of α-casein and α-paracasein are sedimented in 45 min. in the ultracentrifuge. With whole casein and paracasein the amounts are of the same magnitude, but some-what further apart. With low-speed centrifugation, on the other hand, the paracasein was easily sedimented, but the casein almost not at all. Thus, both caseins and paracaseins are highly aggregated, but the latter is stable under the conditions of low-speed centrifugation. The possible role of a protective colloid in the casein-paracasein transformation is discussed. Both α-paracasein and paracasein bind less calcium (9 and 18%, respectively) than do the corresponding caseins.

Adsorption of bovine alkaline phosphatase on diatomaceous silica.

Summary The adsorption of a preparation of bovine alkaline phosphatase on Filter-Cel was investigated in respect to amount of adsorbent, concentration and kind of salt, pH and temperature. Calcined Celites were poor adsorbents for the phosphatase.