title: Solvent proton magnetic resonance dispersion in protocatechuate 3,4-dioxygenase and complexes with 3-halo-4-hydroxybenzoate inhibitors.
abstract: Solvent proton nuclear magnetic dispersion studies at 25, 100, and 300 MHz have been performed on protocatechuate 3,4-dioxygenase (PCD) and its complexes with 3-chloro-4-hydroxybenzoate and 3-fluoro-4-hydroxybenzoate. Longitudinal and transverse relaxation rates were measured for these compounds and for the apoenzyme. The paramagnetic enhancement of solvent T1 is interpreted in terms of dominant dipole-dipole relaxation of fast-exchanging solvent protons with a negligible contribution from outer sphere relaxation and an electronic spin relaxation time of 0.5 ns for the high-spin ferric ion. A discrepancy between the observed T2 at 300 MHz and that calculated by assuming the usual dipolar relaxation provides evidence for an additional Curie-spin dipolar or hyperfine interaction between the proton and iron. Quantitation of the additional relaxivity provides an estimated chemical exchange lifetime of 0.1-0.14 microseconds, which suggests proton exchange by a hydroxide ligand. Proton-to-iron distances are 2.7-3.1 A in PCD and lengthen to 3.6-4.1 A in the halohydroxybenzoate complexes.
mesh_terms: D001051:Apoenzymes / Q000378:metabolism; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D002723:Chlorobenzoates; D005464:Fluorobenzenes; D062385:Hydroxybenzoates / Q000378:metabolism*; D009682:Magnetic Resonance Spectroscopy; D010105:Oxygenases / Q000378:metabolism*; D011520:Protocatechuate-3,4-Dioxygenase / Q000378:metabolism*; D011550:Pseudomonas aeruginosa / Q000201:enzymology*; D012997:Solvents
chemical_list: D001051:Apoenzymes; D002723:Chlorobenzoates; D005464:Fluorobenzenes; D062385:Hydroxybenzoates; D012997:Solvents; C042888:3-fluoro-4-hydroxybenzoate; C042887:3-chloro-4-hydroxybenzoate; D010105:Oxygenases; D011520:Protocatechuate-3,4-Dioxygenase