Proton and iodine-127 nuclear magnetic resonance studies on the binding of iodide by lactoperoxidase
Interaction of an iodide ion with lactoperoxidase was studied by the use of /sup 1/H NMR, /sup 127/I NMR, and optical difference spectrum techniques. /sup 1/H NMR spectra demonstrated that a major broad hyperfine-shifted signal at about 60 ppm, which is ascribed to the heme peripheral methyl protons, was shifted toward high field by adding KI, indicating the binding of iodide to the active site of the enzyme; the dissociation constant was estimated to be 38 mM at pH 6.1. The binding was further detected by /sup 127/I NMR, showing no competition with cyanide. Both /sup 1/H NMR and /sup 127/I NMR revealed that the binding of iodide to the enzyme is facilitated by the protonation of an ionizable group with a pK/sup a/ value of 6.0-6.8, which is presumably the distal histidyl residue. Optical difference spectra showed that the binding of an aromatic donor molecule to the enzyme is slightly but distinctly affected by adding KI. On the basis of these results, it was suggested that an iodide ion binds to lactoperoxidase outside the heme crevice but at the position close enough to interact with the distal histidyl residue which possibly mediates electron transport in the iodide oxidation reaction.
- Research Organization:
- Chiba Univ., Japan
- OSTI ID:
- 5599484
- Journal Information:
- Biochemistry; (United States), Journal Name: Biochemistry; (United States) Vol. 26:20; ISSN BICHA
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
62 RADIOLOGY AND NUCLEAR MEDICINE
ALKALI METAL COMPOUNDS
BARYONS
CATIONS
CHARGED PARTICLES
CHEMICAL SHIFT
CONFIGURATION INTERACTION
ELEMENTARY PARTICLES
ENZYMES
FERMIONS
HADRONS
HALIDES
HALOGEN COMPOUNDS
HEAVY WATER
HYDROGEN COMPOUNDS
HYPERFINE STRUCTURE
INORGANIC PHOSPHORS
INTERMEDIATE MASS NUCLEI
IODIDES
IODINE 127
IODINE COMPOUNDS
IODINE ISOTOPES
IONS
ISOTOPES
MAGNETIC RESONANCE
NMR SPECTRA
NUCLEAR MAGNETIC RESONANCE
NUCLEI
NUCLEONS
ODD-EVEN NUCLEI
OXIDOREDUCTASES
OXYGEN COMPOUNDS
PEROXIDASES
PHOSPHORS
POTASSIUM COMPOUNDS
POTASSIUM IODIDES
PROTONS
RESONANCE
SPECTRA
STABLE ISOTOPES
WATER