Inhibition of Serine β-Lactamases by Vanadate−Catechol Complexes†

All three classes of serine β-lactamases are inhibited at micromolar levels by 1:1 complexes of catechols with vanadate. Vanadate reacts with catechols at submillimolar concentrations in aqueous buffer at neutral pH in several steps, initially forming 1:1, 1:2, and, possibly, 1:3 complexes. Formation of these complexes is followed by the slower reduction of vanadate (VV) to vanadyl (VIV) and oxidation of the catechol. Vanadyl−catechol complexes, however, do not inhibit the β-lactamases. Rate and equilibrium constants of formation of the 1:1 and 1:2 complexes of vanadate with catechol itself and with 2,3-dihydroxynaphthalene were measured by stopped-flow spectrophotometry. Typical examples of all three classes of serine β-lactamases (the class A TEM-2, class C P99, and class D OXA-1 enzymes) were competitively inhibited by the 1:1 vanadate−catechol complexes. The inhibition was modestly enhanced by hydrophobic substituents on the catechol. The 1:1 vanadate complexes are considerably better inhibitors of th...