1. The effect of dilute acids and alkalies on a number of soluble proteins has been studied with regard to (a) the change in solubility; (b) increase in chromogenic value (reducing power towards the phenol reagent of Folin-Denis); and (c) liberation of non-protein substances.
2. All the albumins, globulins, and hemoglobins which we have studied including the albumins of the egg w vhite of duck, goose, hen and pigeon; serum globulins and albumins of sheep and horse; hemoglobins of sheep and pig; and the globulin of hemp seed, edestin, show change in solubility in 0.05-N HCl and NaOH solutions. The solubility of gliadin, zein (in 75% alcohol), gelatin, proteose and peptone is not changed by dilute acids and alkalies.
3. The rate of denaturation, conveniently followed by the amount of insoluble protein obtained on neutralization, varies with different proteins. This may serve for the differentiation of proteins.
4. The hydrogen ion concentration decreases in acid protein solution and the hydroxyl ion concentration decreases in alkaline protein solution.
5. The rate of denaturation increases with increasing hydro-gen ion concentration in acid solution or hydroxyl ion concentra-tion in alkaline solution. An exception is found in horse serum albumin which is denatured in 0.02-N HCI but is stable in 0.05 HCl.
6. The velocity constant K, calculated on the assumption that denaturation is a monomolecular reaction, falls off rapidly with lapse of time. This has been explained by the change in the reaction of the solution.
7. Evidence is adduced to show that the first products of denaturation are insoluble, while the soluble products are formed only secondarily.
8. All the proteins, which become insoluble by the action of acids or alkalies, also show marked increase in chromogenic value. Zein, gliadin, gelatin, proteose and peptone show no appreciable increase in chromogenic value.
9. The form of the chromogenic value-time curve resembles closely that of the denaturation curve. The change in solubility and the increase in chron-iogenic value of proteins are due to the same underlying reaction.
10. The increase in chromogenic value is not due to the formation of new reactive groups towards phenol reagent, but rather to an increase in the reactivity of the protein molecule so that more groups take part in the reaction.
11. The precipitability of the protein by complex acids (e. g., phenol reagent) decreases as the chromogenic v aluein creases.
12. The chromogenic value of the protein denatured by alkali is different from that of the same protein denatured by acid.
13. Ammonia and non-protein chromogenic substances, which are probably tyrosin and tryptophane, are liberated from the pro-tein in 0.05-N NaOH at a measurable rate, but only very slowly in 0.5-N HCl solution. The course of liberation of these subs-tances does not run parallel with that of change in solubility or in chromogenic value. Hydrogen sulphide is also split off from most proteins in alkaline solution, but it forms an inappreciable portion of the non-protein chrornogenic substances. The liberation of these non-protein substances is not an essential feature of the denaturation of proteins.
14. From the increase in the base and acid binding power, and the decrease in precipitability attending the denaturation of proteins it has been concluded that the fundamental reaction underlying the denaturation of proteins by dilute acids and alkalies is a hydrolysis, probably of some especially labile bonds.
15. The products of denaturation of proteins by acids and by alkalies are different.
16. The change in viscosity and conductivity of the alkaline protein solution observed by Schorr is explained by the denatura-tion of the protein.
17. The danger of using acids and alkalies as well as pro-longed dialysis in the preparation of proteins is emphasized.
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