Que L, Epstein R M
Biochemistry. 1981 Apr 28;20(9):2545-9. doi: 10.1021/bi00512a028.
Resonance Raman spectra of a number of protocatechuate 3,4-dioxygenase-inhibitor complexes were studied by use of the available lines of an argon and a krypton laser. Three types of inhibitors were investigated-hydroxybenzoates, dicarboxylates, and 4-nitrocatechol. The hydroxybenzoate study shows that the hydroxy 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 as well as 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 iron; a binding configuration wherein the acidic phenolate group interacts with the carboxylate binding site has been suggested by others. Finally the spectra of the 4-hydroxybenzoate and terephthalate complexes demonstrate the presence of two tyrosines coordinated to the active-site iron as suggested by others; these tyrosines have different vCO's and excitation profiles.
利用氩离子激光器和氪离子激光器的现有谱线，研究了多种原儿茶酸3,4-双加氧酶抑制剂复合物的共振拉曼光谱。研究了三种类型的抑制剂——羟基苯甲酸酯、二羧酸盐和4-硝基儿茶酚。对羟基苯甲酸酯的研究表明，3-羟基苯甲酸酯中的羟基不与活性位点铁配位，这与早期的推测一致，并证实了异构体4-羟基苯甲酸酯中羟基的配位情况。对二羧酸盐的研究表明，戊二酸酯和对苯二甲酸酯都会扰乱活性位点环境，使电荷转移相互作用向更低能量方向移动。对苯二甲酸酯结合的pH依赖性以及二羧酸盐复合物与ESO2中间体的光谱相似性，为该中间体是紧密结合的酶-产物复合物这一推测提供了进一步的证据。对4-硝基儿茶酚的研究表明，与底物儿茶酚不同，4-硝基儿茶酚不与铁结合；其他人曾提出一种结合构型，其中酸性酚盐基团与羧酸盐结合位点相互作用。最后，4-羟基苯甲酸酯和对苯二甲酸酯复合物的光谱表明，如其他人所提出的，有两个酪氨酸与活性位点铁配位；这些酪氨酸具有不同的vCO和激发谱。
