Resonance Raman studies on protocatechuate 3,4-dioxygenase inhibitor complexes

Abstract
Resonance Raman spectra of a number of protocatechuate 3,4-dioxygenase (EC 1.13.11.3)-inhibitor complexes were studied by use of the available lines of an Ar and a Kr laser. (The protocatechuate 3,4-dioxygenase was isolated from Pseudomonas aeruginosa.) Three types of inhibitors were investigated.sbd.hydroxybenzoates, dicarboxylates and 4-nitrocatechol. The hydroxybenzoate study shows that the hydroxyl group in 3-hydroxybenzoate does not coordinate to the active site iron, in agreement with earlier suggestions and confirms the coordination of the hydroxy group in the isomeric 4-hydroxybenzoate. The dicarboxylate study demonstrates that both glutarate and terephthalate perturb the active-site environment, shifting the charge-transfer interaction to lower energy. The pH dependence of terephthalate binding and the spectral similarities of the dicarboxylate complexes to the ESO2 intermediate provides further evidence for the suggestion that this intermediate is a tightly bound enzyme-product complex. The 4-nitrocatechol study indicates that, unlike the substrate catechols, 4-nitrocatechol does not bind to the Fe, a binding configuration wherein the acidic phenolate group interacts with the carboxylate binding site has been suggested by others. The spectra of the 4-hydroxybenzoate and terephthalate complexes demonstrate the presence of 2 tyrosines coordinated to the active-site iron as suggested by others; these tyrosines have different .nu.CO values and excitation profiles.

This publication has 14 references indexed in Scilit: