Studies on the Molecular Mechanism of Mersalyl and 4‐Aminophenylmercuric Acetate Re‐activation of Trypsin‐Thiol Complexes

1. Trypsin has been reacted with dithiothreitol and with a naturally occurring thiol‐containing trypsin inhibitor to form enzyme‐inhibitor complexes. This complex formation is known to be via a reversible intermolecular disulphide linkage. 2. These latent forms of trypsin have been re‐activated with mersalyl [ N ‐( O ‐carboxymethylsalicyloyl)‐3‐hydroxymercuric‐2‐methoxypropylamine], 4‐aminophenylmercuric acetate and with cystine. 3. Active‐site titration analysis of trypsin in the presence of incremental additions of dithiothreitol demonstrated the simultaneous inhibition and modification of the enzyme active site, demonstrating a direct involvement of a significant disulphide controlling the conformation of the active site of the enzyme. 4. Mersalyl addition to the dithiothreitol‐reduced trypsin resulted in a regain of enzymic activity and a corresponding regain of availability of the active sites for titration. 5. Mersalyl and 4‐aminophenylmercuric acetate were shown to re‐activate the trypsin‐inhibitor complex. 6. A molecular mechanism for the organomercurial re‐activation of latent enzymes of this particular type (involving disulphide exchange) has been proposed.