Photoregulation of -chymotrypsin activity by isomerizable inhibitors. Study of the action mechanism.

Abstract

Abstract— The N‐p‐phenylazophenyl‐N‐phenylcarbamyl chloride (PAPC) in its cis form is five times more active as inhibitor of α‐chymotrypsin than in the trans form. In the present work, derivatives of PAPC have been synthesized. Each of these new compounds is photoisomerizable and is an inhibitor (in the cis and in the trans form) of α‐chymotrypsin. The cis isomer is always more active than the trans. The m‐methyl derivative is 17.5 times more active in the cis form than in the trans, whereas, for the para‐substituted compound, this ratio is only 3.5.Several hypotheses can explain this difference of activity between the cis and trans isomers: (1) steric hindrance towards the trans isomer, (2) lower affinity of the enzyme for the trans isomer, (3) higher reactivity of the complex formed between the enzyme and the cis form of the inhibitor. These hypotheses are discussed.