The considerable changes which occur in the behavior of living matter when subjected to high or low temperatures raise interesting questions as to how the temperature affects the behavior of certain substances present in nature.Casein, purified at the point of its maximum flocculation, is able to bind base, forming a salt soluble in water. The amount of casein which passes into solution is not only dependent upon the amount of base added, but also upon the temperature.We propose to study the interdependence of three variables: the base added, the casein dissolved, and the temperature.The properties of casein when dissolved in alkali and combined with base have been studied by a large number of investigators and by different methods. The results obtained may conveniently be considered in terms of the different equivalent combining weights for base that they have ascribed to casein.
The Equivalent Weight of Casein.The combining weight of casein was investigated before the development of the electrolytic dissociation theory. In 1865, Millon and Commaille (1, 2) stated: " . . . la cas6iae, mati~re unique, s'uniralt sans doute A la plupart des acides min6raux et organiques, et si toutes ces combinalsons 6taient r6ellement bien d6finies, il ressortirait de leur 961
1. The preparation and purification of paracasein was described and certain criteria for the absence of free enzyme provided for.
2. The solubility of purified paracasein in water at low temperature was studied, and found practically identical with the solubility of casein.
3. The capacity of paracasein to bind base was investigated by means of its solubility in NaOH at 5° and at 23° ± 2°C., and found to be distinctly different from that of casein.
4. At these two temperature levels paracasein had a 1.5 greater capacity to bind base than casein. The equivalent combining weights of paracasein and casein were found to stand each to the other, apapproximately, as 2 to 3.
5. This relationship suggested that the temperature coefficients of the solubility of paracasein and casein in NaOH are identical.
6. This evidence indicates that paracasein is a modification of casein, distinguishable by physicochemical means.
1. The activity of the hydrogen ion, in a system containing 0.00280 mols of NaAc, 0.520 mols of NaCl per liter, and varied amounts of HCl or NaOH has been investigated. The average value of pK' for acetic add in this system is about 4.37.
2. The effect of the addition of various amounts of HCl and NaOH to a system containing 0.00280 mols of NaAc, 0.520 mols of NaCl, and a known number of cells of either Microciona prolifera or Cliona celata was then studied. It was found that in weak acid solutions Microciona behaves as a stronger base than Cliona, the former being practically saturated with base at a pH of 7.5. Similar behavior is shown by suspensions of cells to which no acid or base was added: the cells of Cliona are more acidic than the cells of Microciona.
3. The microscopic examinations of the cells subjected to the treatment with acid or base indicate that the cells of Microciona remain alive down to pH 4.50; the cells of Cliona sustain greater acidity,— a,t pH 3.7 they exhibit no signs of cytolysis. Tests for aggregation of these cells showed that this phenomenon is greatly inhibited even by slightly acid solutions.
4. The conclusion is drawn that the concentration of cells being equal, the suspensions of cells of Microciona and Cliona differ from each other in their physicochemical properties, the comparison being made on suspensions of specified composition.
In a preceding investigation (1) upon certain properties of paracasein, we attempted to identify paracasein by physicochemical means.Paracaseins were prepared by coagulating milk by means of rennin or pepsin preparations, puri/ying the resulting paracasein in the same way as was done in the case of casein (2). Such preparations, free from any proteolytic enzyme, were then tested for their solubility in water and for their solubility in dilute NaOH solutions at two temperatures. It was found that although paracasein at about 6°C. dissolves in water to the same extent as casein, the capacity to bind base was distinctly different from that of casein. While casein at 21 to 37°C. dissolves in combination with base to the extent of about 2100 gm. per tool of NaOH added (2, 3), most of the paracasein preparations combined with NaOH in this temperature range with a combining weight of 1450 gm.The ratio of the equivalent combining weight of casein to the combining weight of paracasein is as 1 to 1.45. Solubility measurements at 5°C. indicated that the same relationship held true for these proteins at low temperature.In the present investigation, we have studied further some of the other properties of paracasein preparations, among which are the hydrogen ion activity in systems composed of paracasein and base, and the maximum base-binding capacity of certain paracaseins.
scite is a Brooklyn-based startup that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.