Reversible binding of peptide aldehydes to papain. Structure-activity relationships.

摘要: Abstract The hydration of eleven peptide and hippuryl aldehydes has been measured as a function temperature by means NMR spectroscopy. In all cases the were strongly hydrated (i.e., 90–95%) in aqueous solution. Dehydration hydrates was endothermic, but this partly offset positive entropy for dehydration. binding to papain fluorescence titration, from these data dissociation constants hemithioacetal enzyme adducts derived. Binding N-Ac- l -PheNHCH2CHO (1) particularly tight (Kd,corr = 0.00043 μM) whereas that its d -enantiomer (2) 300-fold weaker 0.129 μM). correlated with those reversible covalent analogous nitriles according equation log Kd(CHO) −2.687 + 1.016 Kd,corr(CN) (r 0.99), lending support previous suggestions both behave transition-state- or reactive intermediate analogs papain. This finding is striking view obvious differences hybridization (sp2 vs. sp3) geometry (trigonal tetrahedral) at P1 carbon center their adduct forms (thioimidate ester hemithioacetal, respectively). A model substrates, transition states thereof proposed. key feature an obligatory (or developing covalent) interaction between Cys-25-SH carbonyl equivalent P1, augmented intermolecular P1NH OC(Asp-158), P2CO HN(Gly-66) P2NH OC(Gly-66) hydrogen bonds hydrophobic P2 S2 interaction. latter three interactions are optimum nearly when -amino acid N-acyl substituent. Data presented suggest derivatives relatively non-specific substrates inhibitors and, consequently, diminished value probes catalytic studies.