PKOTEINS OR ALBUMINOUS SUBSTANCES 429 



When the anhydride is warmed with hydrochloric or hydro- 

 bromic acid or with dilute alkali, the elements of water are taken 

 up and the dipeptide results ; thus 



A step by which the higher stages of condensation are reached 

 consists in first forming a compound of the lower peptide with 

 the chloride of an acid radicle, such as acetyl chloride, containing 

 an atom of halogen, e.g. chloracetyl chloride CH 2 C1-CO-C1. In 

 such case HC1 is eliminated and a compound is formed which, 

 by the action of ammonia, exchanges Cl for NH 2 and the poly- 

 peptide results. Thus glycyl-glycine gives chloracetyl-glycyl- 

 glycine 



CH 2 C1-CO-NH-CH 2 -CO-NH-CH 2 -CO-OH 



which yields diglycyl-glycine (a tripeptide) 



CH 2 NH 2 -CO-NH-CH 2 -CO-NH-CH 2 -CO-OH 



Proceeding on similar lines more complex molecules are built 

 up by making use of other amino-acids, such as aspartic acid 



HO-CO-CH 2 -CHNH 2 -CO-OH 



the acid derived from asparagine, a crystalline, soluble amide 

 which occurs commonly in plants. Aspartic acid is also found 

 among the products of the degradation of proteins. 



More than one hundred of the artificial polypeptides have 

 been produced by similar methods. Fischer has described the 

 preparation of an octo decapeptide, derived from fifteen molecules 

 of glycine and three molecules of Meucine, which in its external 

 properties closely resembles many natural proteins. Thus 

 penta glycyl glycine was allowed to react with d-biomo-iso 

 capronyl diglycyl-glycyl chloride and the product so obtained 

 was treated with ammonia with formation of Meucyl octo glycyl 

 glycine. By a repetition of this series of reactions the octo deca- 

 peptide, Meucyl triglycyl Meucyl triglycyl Meucyl octo glycyl 

 glycine is produced, The formula of this is given on the 

 following page. 



