Proton and nitrogen-15 NMR spectroscopic studies of hydrogen ion-dependent pseudo-halide ion binding to chloroperoxidase
The proton nuclear magnetic resonance spectra of several chloroperoxidase-inhibitor complexes have been investigated. Titrations of chloroperoxidase with azide, thiocyanate, cyanate, or nitrite ions indicate that only the chloroperoxidase-thiocyanate complex exhibits slow ligand exchange on the 360-MHz NMR time scale. The temperature dependence of the proton NMR spectra of the complexes suggests that, although the complexes are predominantly low-spin ferric heme iron, a spin equilibrium is present presumably between S = 1/2 and S = 5/2 states. The pH dependence of the proton NMR spectra of the psuedo-halide-chloroperoxidase complexes was examined at 360 and 90 MHz. Chloroperoxidase complexes with azide and cyanate show similar behavior; 360-MHz proton spectra are readily observed at low pH (less than 5.0) but not at high pH. At high pH, the ligand exchange rate falls in an intermediate time range. When the complexes are examined at 90 MHz, however, spectra consisting of averaged signals are observed. The chloroperoxidase-thiocyanate complex does not form at high pH values; the proton NMR spectrum observed is that of native chloroperoxidase. The pKa for the chloroperoxidase-thiocyanate heme-linked ionizable amino acid residue falls between 4.2 and 5.0. Only an averaged azide signal was observed in the nitrogen-15 NMR spectra for solutions that contained the azide complex of chloroperoxidase, horseradish peroxidase, and myoglobin.
- Research Organization:
- Univ. of Iowa, Iowa City
- OSTI ID:
- 6840462
- Journal Information:
- J. Biol. Chem.; (United States), Journal Name: J. Biol. Chem.; (United States) Vol. 35; ISSN JBCHA
- Country of Publication:
- United States
- Language:
- English
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560300* -- Chemicals Metabolism & Toxicology
59 BASIC BIOLOGICAL SCIENCES
63 RADIATION, THERMAL, AND OTHER ENVIRON. POLLUTANT EFFECTS ON LIVING ORGS. AND BIOL. MAT.
ANIMALS
ANIONS
ANTITHYROID DRUGS
AZIDES
BARYONS
BIOCHEMICAL REACTION KINETICS
BODY
CARBONIC ACID DERIVATIVES
CARBOXYLIC ACIDS
CARDIOVASCULAR SYSTEM
CHARGED PARTICLES
CHEMICAL BONDS
COMPLEXES
CYANATES
DRUGS
ELEMENTARY PARTICLES
ENZYME INHIBITORS
ENZYMES
FERMIONS
GLOBIN
HADRONS
HEART
HETEROCYCLIC ACIDS
HETEROCYCLIC COMPOUNDS
HORMONE ANTAGONISTS
HORSES
IONS
ISOTOPES
KINETICS
LIGHT NUCLEI
MAGNETIC RESONANCE
MAMMALS
MUSCLES
MYOCARDIUM
MYOGLOBIN
NITRITES
NITROGEN 15
NITROGEN COMPOUNDS
NITROGEN ISOTOPES
NMR SPECTRA
NUCLEAR MAGNETIC RESONANCE
NUCLEI
NUCLEONS
ODD-EVEN NUCLEI
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
ORGANIC SULFUR COMPOUNDS
ORGANS
OXIDOREDUCTASES
OXYGEN COMPOUNDS
PEROXIDASES
PIGMENTS
PORPHYRINS
PROTEINS
PROTONS
REACTION KINETICS
RESONANCE
SPECTRA
STABLE ISOTOPES
THERMODYNAMICS
THIOCYANATES
VERTEBRATES