Enantioselective and Reversible Inhibition of Trypsin and α-Chymotrypsin by Phosphonate Esters

Qinjian Zhao, Ildiko M. Kovach, A. Bencsura, Adonia Papathanassiu

Research output: Contribution to journalArticle

32 Citations (Scopus)

Abstract

Trypsin is inactivated by the levorotatory enantiomers (most likely PS) of 4-nitrophenyl 4-H-, 4-CH3-, 4-OCH3-, and 4-Cl-phenacyl methylphosphonates (PMNs) with second-order rate constants between 231 and 884 M−1 s−1. 4-NO2-PMN hydrolyzes before inhibiting the enzyme. The second-order rate constants for the inactivation of α-chymotrypsin by the levorotatory enantiomers of the five PMNs are between 37 000 and 770 000 M−1 s−1, and those for the dextrorotatory enantiomers are between 400 and 640 M−1 s−1; the enantioselectivity is 90–1880. Specific rotation [α]22D of the faster-reacting enantiomer of 4-CH3-PMN with trypsin and α-chymotrypsin is −30 ± 6°. 31P NMR of the adducts shows a signal at 41.0 ppm, 10 ppm downfield from the parent compound. Results of molecular mechanics and dynamics calculations show that the principal interactions are between the phosphonyl group and constituents of the oxyanion hole and between the aromatic fragment and residues in the binding regions of the enzymes. Trypsin activity returns from its phenacyl methylphosphonyl adducts on the hour time scale and in reversed order to the rates of inactivation within the series. Recovery of α-chymotrypsin activity from the adducts formed with the (−) enantiomers is on a slower time scale still, whereas its recovery from the adducts formed with the (+) enantiomers is on the second to minute time scale. The data support a mechanism of reactivation involving rate-determining intramolecular displacement of Ser by the carbonyl hydrate of the phenacyl moiety. The pH-rate profiles for trypsin reactivation from its adducts indicate involvement of an ionizable group with pKa ∼ 8.0. The pH dependence and solvent isotope effects are small in most cases. The compounds demonstrate favorable properties for controllable and temporary modulation of enzyme activity.

Original languageEnglish
Pages (from-to)8128-8138
Number of pages11
JournalBiochemistry
Volume33
Issue number26
DOIs
Publication statusPublished - Jul 1 1994

ASJC Scopus subject areas

  • Biochemistry

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