Serine protease inhibitors affinity labels

Serine Protease Inhibitors. The two major catalytic residues of serine proteases are a serine residue and a histidine residue. Affinity labels have been developed that modify both of these residues. 

The most interesting class of protease inhibitors in viral studies has been the chloromethyl ketone derivatives of amino acids (54j 55) These were designed as affinity labels of serine-type proteases, and react irreversibly with histidine and serine residues in the active sites of proteases. There is a basis for selectivity of the chloromethyl ketones phenylalanyl and lysyl derivatives were synthesized, which had specificity for chymotrypsin and trypsin, respectively (54) This specificity led to studies on inhibition of poliovirus protein cleavage, with positive results (25, 26). 

Representative examples of halomethyl ketones which have been used as affinity labels for serine proteases are listed in the table. Several thiol proteases (papain, clostripain, cathepsin B, and cocoonase) are also listed since the mechanism of the inhibition is probably similar for the two classes of enzymes. The inhibitors chosen for the table were either the most readily available or among the more reactive for a particular enzyme. For more information the reader is referred to a recent comprehensive review of all the enzymes that have been studied with halomethyl ketone inhibitors. ... 

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