474 LECTURE XX. 



least one asymmetric carbon atom. Now it was of great interest to trace 

 the behavior of the synthetic polypeptides in the presence of proteolytic 

 ferments, in order to ascertain whether the fine distinctions which were 

 noticed with the carbohydrates would also apply here. The synthetic 

 polypeptids do, in fact, show a decidedly different behavior toward the 

 pancreatic juice, as is shown by the following table: * 



The -Pancreatic Juice 



Hy droly zes : Does not hy drolyze : 



* Alanyl-glycine Glycyl-alanine 

 *Alanyl-alanine Glycyl-glycine 



* Alanyl-leucine A Alanyl-leucine B 

 *Leucyl-isoserine A Leucyl-alanine 



Glycyl-Z-tyrosine Leucyl-glycine 



Leucyl-Z-tyrosine Leucyl-leucine 



*Alanyl-glycyl-glycine Aminobutyryl-glycine 



*Leucyl-glycyl-glycine Aminobutyryl-aminobutyric acid A 



*Glycyl-leucyl-alanine Aminobutyryl-aminobutyric acid B 



*Alanyl-leucyl-glycine Aminoisovaleryl-glycine 



Dialanyl-cystine Glycyl-phenylalanine 



Dileucyl-cystine Leucyl-proline 



Tetraglycyl-glycine Diglycyl-glycine 



Triglycyl-glycine-ester Triglycyl-glycine 



( = Curtius' Biuret-base.) Dileucyl-glycyl-glycine 



If we examine these two columns, we observe that the pancreatic fer- 

 ment has various points of attack. In the first place, the structure of the 

 individual compounds must be taken into consideration. A good example 

 here is the behavior of alanyl-glycine: 



CH 3 . CH(NH 2 ) . CO . NH . CH 2 . COOH, 

 and its isomer, glycyl-alanine: 



NH 2 . CH 2 . CO . NH . CH(CH 3 ) . COOH. 



The former is hy droly zed, the latter is not. The nature of the individual 

 amino acid is also important. Thus, those dipeptides are susceptible to 

 hydrolysis in which the alanine acts as acyl, examples being: alanyl- 

 glycine, alanyl-alanine, alanyl-leucine. The hydroxy acids, tyrosine and 

 isoserine, have a similar effect when they are at the end of the chain. It is 



1 Emil Fischer and Emil Abderhalden: Z. physiol. Chem. 46, 52 (1905). Compare 

 also, Sitzber. Kgl. Preuss. Akad. Wiss. 10 (1905), and Emil Fischer and Peter Bergell: 

 Ber. 36, 2592 (1903); 37, 3103 (1904). 



