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.