J. S. FRUTON 



same type of specificity and split the same synthetic substrates as does 

 crystalline pancreatic trypsin. Because of this relationship, the 

 members of this group of enzymes have been designated "trypsinases." 

 Similarly, evidence has been obtained for the existence of groups of 

 enzymes related in specificity to pepsin, to leucine aminopeptidase, 



Table II 

 Specificity of Proteolytic Enzymes 



Enzyme 



Requisite groups in substrate 

 backbone 



Requisite groups in 

 substrate side chain 



Peptidases (Exopepiidases) 



Leucine aminopeptidase from in- 

 testinal mucosa, beef spleen, 

 beef kidney, and swine kidney 



Chymotrypsin aminopeptidase 



Other aminopeptidases 



Carboxypeptidase from pancreas, 

 beef spleen, beef kidney, and 

 swine kidney 



Other carboxypeptidases 



R 



I 

 NHiCHCO^NH... 



Same 



Same 



R 



I 

 . . .CO^NH-CH-COOH 



Same 



CHi 

 CHi 



\CH • CH2 . 



HO-C6H4CH2. 



or 

 C8H6CH2... 



HGCsHi-CHj. 



or 

 CeHsCHj... 



Proteinases (Endopeptidases) 



Pepsin 



Pepsinases from beef spleen, beef 

 kidney, and swine kidney 



Trypsin 



Tripsinases from beef spleen, beef 

 kidney, swine kidney, and 

 papain 



Chymotrypsin 



R 



: I 



. . CO—NH- CHK-CO^J^H- CH . 



. CO—NH- CH- CO -^NH . . . 



R 



I 

 . . . CO—NH- CH • CO^NH . . . 



HO.C6H4CH2... 



or 

 CeHs-CHj... 



NH2-CH2(CH2)a.. 



or 

 NHj. 



>C.NH.(CH2)3 



HOC6H4CH2... 



or 

 C6H6CH2... 



and to crystalline pancreatic carboxypeptidase. These are referred 

 to as "pepsinases," "leucine aminopeptidases," and "carboxypep- 

 tidases," respectively. Such groups of enzymes possessing identical 

 backbone and side-chain requirements are termed homospecific 

 enzymes (6) . On the other hand, two enzymes which diflfer from one 

 another with respect to their backbone or side-chain requirements, 

 or both, are designated heterospecific enzymes. 



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