Tosyl-L-phenylalanine chloromethylketone

N-tosyl-L-phenylalanine ethyl ester (Formula 2.18) is a suitable substrate for the proteinase chymotrypsin which hydrolyzes ester bonds. When the ethoxy group is replaced by a chloro-methyl group, an inhibitor whose structure is similar to the substrate is formed (Na-tosyl-L-phenylalanine chloromethylketone, TPCK). 

The principles of the method can be illustrated by one of the first affinity labeling experiments developed by E. Shaw, the reaction of JV-tosyl-L-phenylalanine chloromethylketone (TPCK) with a-chymotrypsin (314). 

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