Chinese Journal of Physiology

Lo

HSIEN WU

If egg albumin is first heated in a slightly acid or alkaline solution so that the denatured albumin remains in solutlon, and then the solution is cooled and neutralized, the protein which flocculates is readily redissolved by a slight excess of acid or alkali. If, however, the egg albumin is heated in a solution of such hydrogen ion concentration that flocculation occurs during the heating, the product obtained is practically insoluble in dilute acids and alkalies. Evidently, then, there is a difference between the albumin which has been separately denatured and flocculated and that which has been coagulated in one operation. For the sake of brevity we will call the former flocculated albumin in this paper. Chick and Martin (8) also recognized the difference between the flocculated and the coagulated albumins, but they were inclined to the view that they represent different forms of the same chemical individual. They believed that the different degrees of cohesion of the particles would account for the difference in solubility. This view does not seem to be correct, since the difference in solubility between the flocculated and the coagulated egg albumins is not merely quantitative but qualitative. The coagulated protein will not dissolve, even on long standing, in such solutions of dilute acids or alkalies as will just completely dissolve the flocculated protein.

There is also a difference in physical appearance between the flocculated and the coagulated egg albumin. The former is fluffy and more or less transparent while the latter is granular and opaque. If the flocculated albumin is heated, it loses its solubility in dilute acids and alkalies and becomes indistinguishable in physical appearance from that of the coagulated albumin.

We have recently observed another difference between flocculated albumin and coagulated albumin in the course of a study of their molecular weight.* Burk and Greenberg (1) have shown that concentrated urea solutions exert a powerful solvent action on proteins which are insoluble in water at the isoelectric point, and they have suggested the use of this solvent for the determination of molecular weight of proteins. In applying this method to flocculated and coagulated egg albumins we found the former to be soluble, while the latter insoluble, in 49 per cent urea solution. Flocculated albumin after heating in the isoelectric region also becomes insoluble. Albumin which has been denatured by alcohol and then flocculated by neutralization is soluble, but that coagulated by alcohol is insoluble. Albumin coagulated

This work is in progress and will be reported later,