Chinese Journal of Physiology

4 HSIEN WU

tion, then we may conclude that denaturation of egg albumin does not occur when it is heated at the isoelectric point for a short time. In other words, the albumin coagulated at the isoelectric point has not undergone denaturation,

That proteins can be coagulated by shaking which does not cause or accelerate denaturation (10) also supports the view that coagulation is independent of denaturation. We assumed previously that denaturation preceds coagulation by shaking. This assumption was necessary as long as coagulation was regarded as the sum of denaturation and flocculation. With the adoption of the new concept of coagulation, that assumption is no longer required.

It is interesting to record in this connection an observation on the effect of alcohol on denatured albumin. Although alcohol and shaking as well as heat can coagulate the natural egg albumin, only heat can coagulate denatured egg albumin, suspended in an isoelectric solution, while alcohol and shaking have no effect. The denatured egg albumin is thus more difficult to coagulate than the natural egg albumin. This would be contrary to our expectation if denaturation is a necessary preliminary to coagulation, but it harmonizes well with the view that denaturation and coagulation are two separate processes of opposite nature.

We may define denaturation, flocculation and coagulation as follows :—

(1) Denaturation is that change of the natural protein, brought about by the action of acids or alkalies, whereby it becomes insoluble in solvents in which it was previously soluble. Denaturation is slow in the isoelectric region of the protein, but it may be accelerated by heat or alcohol.

(2) Flocculation is the precipitation of the denatured protein from solution by bringing the reaction of the solution to the isoelectric region of the denatured protein. Flocculation may be compared with the precipitation of an insoluble acid or base from a solution of its soluble salt,

(3) Coagulation is that change characterized by decrease of solubility of the natural or denatured protein, brought about by the action of heat, alcohol, shaking etc., in the isoelectric region of the protein.

The relation between the three processes is shown in the following diagram,