CHAPTER XXV 

 PROTEINS 



On several occasions, reference has been made to the proteins 

 as the most important constituents of protoplasm. While it is 

 impossible to single out any one necessary substance as the 

 most important in a system, yet, as Pauli has said, the proteins, 

 more than any other group of substances, display those proper- 

 ties which combined we call life. Obviously, then, a study of 

 them must yield very important deductions in the physics and 

 chemistry of protoplasm. 



Emil Fischer regarded the proteins as taking part, in one way 

 or another, in all jjhysiological processes in the living organism. 



The early study of proteins was by classical chemical methods. 

 Only recently has the colloid chemist carried the study of them 

 into the world of physics. Among the first to do this were the 

 Scandinavian S. P. L. S0rensen and the Austrian physician 

 Wolfgang Pauli. It is our task to consider the physical proper- 

 ties — in particular, the structure — of the proteins. It was 

 an elucidation of their structure that Emil Fischer advocated 

 in pointing out the significance of the study of proteins in 

 biological chemistry. But before the physical aspects of protein 

 behavior can be satisfactorily considered, some knowledge of 

 their chemical constitution must be had. For this, we turn to 

 the organic chemists. 



Classification. — A classified list, with examples, will convey 

 an idea of the kind of substances that proteins are better than 

 will a definition. The English classification has the advantage 

 of simplicity; with sKght modifications, it is as follows: 



I. Simple proteins — These are naturally occurring proteins which are 

 hydrolyzed only by enzymes or acids into a-amino acids or their 

 derivatives 



A. Protamines — salmin from salmon sperm 



B. Histones — globin from hemoglobin 



C. Globulins — ovoglobulin from egg yolk 



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