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.
journal_name
Biochemistryjournal_title
Biochemistryauthors
Felton RH,Gordon SL,Sowell AL,May SWdoi
10.1021/bi00312a024subject
Has Abstractpub_date
1984-08-14 00:00:00pages
3955-9issue
17eissn
0006-2960issn
1520-4995journal_volume
23pub_type
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