ON HEAT COAGULATION OF PROTEINS. 281 



On Heat Coagulation of Proteins. By Harriette Chick, D.Sc, and 

 C. J. Martin, M.B., D.Sc, F.R.S. 



[Ordered by the General Committee to be printed in cxtcnso.] 



On heating solutions of many proteins an irreversible change of state 

 occurs, so-called 'heat coagulation.' It has been the practice to re- 

 gard the temperature at which this occurs as if it were a physical con- 

 stant characteristic of the particular protein, although Duclaux and 

 others have criticised this view. 



This manner of regarding the matter is entirely misleading, for, as 

 will be shown, ' heat coagulation ' is a reaction between the protein 

 and hot water in which heat plays the merely subsidiary part of an 

 accelerator. 



Heat coagulation consists of two separate phenomena — (1) a 

 chemical transaction between protein and water (denaturation) ; (2) a 

 subsequent aggregation of the altered protein complexes so as to form 

 a precipitate (agglutination) or gel. The second stage may be in abey- 

 ance, although the first has occurred. By adjusting the conditions we 

 have been able to study these two stages in the process apart from 

 each other. 



Denaturation. 



Water as such, or in the form of steam, is essential for denatura- 

 tion, for proteins in the dry condition can be heated to 150° C. (Michel 

 and Wichmann) without change. We found that crystallised egg alb. 

 suffered no change on heating to 120° 0. for five hours in the dry state, 

 and that methsemoglobin was unaltered after four hours at 110° C. 



The reaction rate of denaturation. 



Protein sols were placed in a test tube of 200 c.c. capacity, fitted 

 with a stirrer of bent glass tube. The upper end of the stirrer passed 

 through a glass bearing in the rubber cork and served also for the 

 withdrawal of samples. The whole apparatus was immersed in a ther- 

 mostat, which could be maintained at any desired temperature. 



At definite intervals after the solutions had taken the temperature 

 of the bath, samples were withdrawn and the content of protein still 

 in solution determined. 



The conditions of the experiments were so adjusted that the second 

 process — agglutination of the denaturated protein — had a much higher 

 velocity than the denaturation, so that the rate of this latter was the 

 limiting factor. 



Two proteins, haemoglobin and egg albumen, both of which had been 

 purified by re-crystallisation, were investigated. In the case of the 



