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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.

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The use of a halogenated phthalein dye for the investigation of hepatic function was first proposed by Rowntree, Hurwitz and Bloomfield (1) in 1913. Their technique required the measurement of the fecal excretion of phenoltetrachlorphthalein following its parenteral administration. However, it was subsequently shown by Rosenthal and White (2) that intravenously administered phenoltetrabromophthalein disulfonate (BSP) is removed from the blood almost exclusively by the liver and that the function of the liver may therefore be evaluated by measuring the rate of disappearance of this dye from the plasma.Various lines of evidence support the view that the removal of BSP (and presumably many other substances) from the plasma involves two processes: 1) storage of the material in the liver and 2) biliary excretion. Following the intravenous administration of BSP to dogs it was first shown by Wirts and Cantarow (3) that the output of BSP in the bile continues for over three hours after its virtual disappearance from the plasma, indicating that this material is first taken up by the liver and then gradually excreted. This observation was confirmed by Brauer and Pessotti (4), also in dogs. The existence of a similar hepatic BSP storage mechanism in man is evident from the studies of Mendeloff, Kramer, Ingelfinger and Bradley (5) in which a retardation of the BSP disappearance rate from plasma was noted when successive identical intravenous dosts were administered 30 minutes apart.

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