1984
DOI: 10.1021/bi00312a024
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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 relaxat… Show more

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Cited by 8 publications
(10 citation statements)
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“…First, the Lewis acidity of a 5-coordinate ferric ion with two neutral nitrogen ligands is expected to be large enough to lower the pKz of a coordinated water molecule and result in its deprotonation at neutral pH; note, for example, the ready formation of oxo-bridged complexes of bis(salicylidenamine)iron(III) (Mukherjee et al, 1988;Murray, 1974). Second, NMR water relaxation studies on 3,4-PCD from P. aeruginosa are consistent with the presence of a single proton 2.7 A from the iron center (Felton et al, 1984), which is at the appropriate distance for the proton on a coordinated hydroxide. Taken together, these observations suggest that the coordinated solvent in 3,4-PCD is a coordinated hydroxide rather than water.…”
Section: Resultsmentioning
confidence: 69%
“…First, the Lewis acidity of a 5-coordinate ferric ion with two neutral nitrogen ligands is expected to be large enough to lower the pKz of a coordinated water molecule and result in its deprotonation at neutral pH; note, for example, the ready formation of oxo-bridged complexes of bis(salicylidenamine)iron(III) (Mukherjee et al, 1988;Murray, 1974). Second, NMR water relaxation studies on 3,4-PCD from P. aeruginosa are consistent with the presence of a single proton 2.7 A from the iron center (Felton et al, 1984), which is at the appropriate distance for the proton on a coordinated hydroxide. Taken together, these observations suggest that the coordinated solvent in 3,4-PCD is a coordinated hydroxide rather than water.…”
Section: Resultsmentioning
confidence: 69%
“…(ii) Many monohydroxy inhibitor complexes of 3,4-PCD are also composed of several spectroscopically distinct species, although they form more homogeneous complexes than substrates. (iii) Transient stopped flow kinetics show that hydroxynicotinic acid N -oxide inhibitor binding to wild-type 3,4-PCD (Whittaker & Lipscomb, 1984a) and PCA binding to the Tyr447 → His mutant 3,4-PCD occurs in at least four discrete steps, yielding intermediates with dramatically different spectroscopic properties. Although the complexes of this study do not directly reveal a progression of binding orientations from a low-affinity to a high-affinity orientation in one complex, we propose that the range of binding orientations for the family of substrate-like inhibitor molecules are consistent with orientations that can be reasonably expected as substrate binds to the enzyme.…”
Section: Discussionmentioning
confidence: 99%
“…The walls of the active site cleft are formed primarily by residues from the R-and β-subunits within each protomer, although portions of the outer rim are composed of residues from 2-fold and 3-fold related protomers. Two tyrosinates (Tyr408 and Tyr447), 3 two histidines (His460 N 2 and His462 N 2 ), and an exogenous solvent molecule (Wat827), thought to be a Biochemistry 1997, 36, 10039-10051 S0006-2960(97)00468-6 CCC: $14.00 © 1997 American Chemical Society hydroxide ion (Felton et al, 1984;True et al, 1990), ligate the Fe 3+ to yield approximate trigonal bipyramidal coordination geometry as illustrated in Scheme 1. There is a significant distortion of the iron coordination sphere toward octahedral geometry illustrated by the 93°Tyr408 Oη -Fe 3+ -His460 Ν 2 equatorial bond angle.…”
mentioning
confidence: 99%
“…3 As shown in Scheme 1, inset, Tyr447 Oη and His462 N 2 provide the axial ligands, and Tyr408 Oη and His460 N 2 provide two of the equatorial ligands. Wat827, an exogenous solvent molecule thought to be hydroxide ion (True et al, 1990;Felton et al, 1984), completes the equatorial plane.…”
mentioning
confidence: 99%