Binding of thiocyanate to lactoperoxidase: 1H and 15N nuclear magnetic resonance studies
- Tata Institute of Fundamental Research, Bombay (India)
The binding of thiocyanate to lactoperoxidase (LPO) has been investigated by 1H and 15N NMR spectroscopy. 1H NMR of LPO shows that the major broad heme methyl proton resonance at about 61 ppm is shifted upfield by addition of the thiocyanate, indicating binding of the thiocyanate to the enzyme. The pH dependence of line width of 15N resonance of SC15N- in the presence of the enzyme has revealed that the binding of the thiocyanate to the enzyme is facilitated by protonation of an ionizable group (with pKa of 6.4), which is presumably distal histidine. Dissociation constants (KD) of SC15N-/LPO, SC15N-/LPO/I-, and SC15N-/LPO/CN- equilibria have been determined by 15N T1 measurements and found to be 90 +/- 5, 173 +/- 20, and 83 +/- 6 mM, respectively. On the basis of these values of KD, it is suggested that the iodide ion inhibits the binding of the thiocyanate but cyanide ion does not. The thiocyanate is shown to bind at the same site of LPO as iodide does, but the binding is considerably weaker and is away from the ferric ion. The distance of 15N of the bound thiocyanate ion from the iron is determined to be 7.2 +/- 0.2 A from the 15N T1 measurements.
- OSTI ID:
- 5482261
- Journal Information:
- Biochemistry; (USA), Journal Name: Biochemistry; (USA) Vol. 28:11; ISSN 0006-2960; ISSN BICHA
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
59 BASIC BIOLOGICAL SCIENCES
AMINO ACIDS
ANTITHYROID DRUGS
AZOLES
BARYONS
BIOCHEMICAL REACTION KINETICS
CARBONIC ACID DERIVATIVES
CARBOXYLIC ACIDS
CHEMICAL SHIFT
DRUGS
ELEMENTARY PARTICLES
ENZYMES
FERMIONS
HADRONS
HEME
HETEROCYCLIC ACIDS
HETEROCYCLIC COMPOUNDS
HISTIDINE
HORMONE ANTAGONISTS
IMIDAZOLES
ISOTOPE APPLICATIONS
ISOTOPES
KINETICS
LIGHT NUCLEI
MAGNETIC RESONANCE
MEMBRANE PROTEINS
NITROGEN 15
NITROGEN ISOTOPES
NMR SPECTRA
NUCLEAR MAGNETIC RESONANCE
NUCLEI
NUCLEONS
ODD-EVEN NUCLEI
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
ORGANIC SULFUR COMPOUNDS
OXIDOREDUCTASES
PEROXIDASES
PIGMENTS
PORPHYRINS
PROTEINS
PROTONS
REACTION KINETICS
RECEPTORS
RESONANCE
SPECTRA
STABLE ISOTOPES
THIOCYANATES
TRACER TECHNIQUES