PHYSIOLOGICAL CHEMISTRY 



the protein with hydrochloric acid) by fractional distillation of their 

 ethereal salts under greatly reduced pressure. It will be noticed that the 

 figures given for any one protein do not by any means add up to 100 %. 

 This is due to the occurrence of some inevitable loss in the method of 

 separation, and to the fact that doubtless all the components of protein 

 have not yet been isolated. 



The results of the synthetic method of procedure have also been 

 highly interesting. This has been mainly the work of Emil Fischer 

 and his pupils. Starting with a simple end product, such as glycin, 

 monamino-acetic acid, two of these are combined together, forming a 

 da-peptide glycyl-glycin with the elimination of water, thus : 



OH 

 NH 2 CH 2 CO 



H 



NHCH 2 COOH = NH 2 CH 2 CO.NHGH 2 COOH + H 2 0. 



Glycin. Glycin. Glycyl-glycin. 



The addition of another molecule forms a tripeptide, and so on until 

 potypeptides (many linkages) are formed. Pentaglycyl-glycin, for 

 example, is : 



NH 2 CH 2 CO(NHCH 2 CO) 4 NHCH 2 COOH. 



But not only has glycin been combined to glycin other end products, 

 such as alanin, leucin, phenylalanin, tyrosin, etc., have been combined 

 together, giving such bodies as leucyl-glycyl-alanin, and so on. For 

 example, the polypeptide (do-deka-peptide) leucyl-deca-glycyl-glycin 

 has the formula : 



C 4 H 9 CH(NH 2 )CO 



Leucyl. 



(NHCH 2 CO) 10 

 Glycyl. 



NHCH 2 COOH. 



Glycin. 



By many such operations, polypeptides have been obtained, which, if 



