Electron paramagnetic resonance studies on conformation states and metal ion exchange properties of vanadium bromoperoxidase

Journal Article · Tue Mar 08 00:00:00 EST 1988 · Biochemistry; (United States)

OSTI ID:5272452

de Boer, E; Boon, K; Wever, R

An electron paramagnetic resonance (EPR) study was carried out to examine structural aspects of vanadium-containing bromoperoxidase from the brown seaweed Ascophyllum nodosum. At high pH, the reduced form of bromoperoxidase showed an apparently axially symmetric EPR signal with 16 hyperfine lines. When the pH was lowered, a new EPR spectrum was formed. When EPR spectra of the reduced enzyme were recorded in the pH range from 4.2 to 8.4, it appeared that these changes were linked to a functional group with an apparent pK/sub a/ of about 5.4. In D/sub 2/O this value for the pK/sub a/ was 5.3. It is suggested that these effects arise from protonation of histidine or aspartate/glutamate residues near the metal ion. The values for the isotropic hyperfine coupling constant of the reduced enzyme at both high and low pH are also consistent with a ligand field containing nitrogen and/or oxygen donor atoms. When reduced bromoperoxidase was dissolved in D/sub 2/O or H/sub 2//sup 17/O instead of H/sub 2//sup 16/O, vanadium (IV) hyperfine line widths were markedly affected, demonstrating that water is a ligand of the metal ion. Together with previous work these findings suggest that vanadium (IV) is not involved in catalytic turnover and confirm the model in which the vanadium (V) ion of the native enzyme only serves to bind both hydrogen peroxide and bromide. After excess vanadate was added to a homogeneous preparation of purified bromoperoxidase, the extent of vanadium bound to the protein increased from 0.5 to 1.1, with a concomitant enhancement of enzymic activity. Finally, it is demonstrated that both vanadate (VO/sub 4//sup 3 -/) and molybdate (MoO/sub 4//sup 2 -/) compete for the same site on apobromoperoxidase.

• Research Organization: Univ. of Amsterdam (Netherlands)
• OSTI ID: 5272452
• Journal Information: Biochemistry; (United States), Vol. 27:5
• Country of Publication: United States
• Language: English

Related Subjects

59 BASIC BIOLOGICAL SCIENCES
MOLYBDATES
BIOCHEMISTRY
PEROXIDASES
ELECTRON SPIN RESONANCE
STRUCTURAL CHEMICAL ANALYSIS
VANADATES
CATIONS
ELECTRON SPECTRA
HEAVY WATER
HYPERFINE STRUCTURE
LIGANDS
ORGANIC BROMINE COMPOUNDS
OXYGEN 17
PH VALUE
WATER
CHARGED PARTICLES
CHEMISTRY
ENZYMES
EVEN-ODD NUCLEI
HYDROGEN COMPOUNDS
IONS
ISOTOPES
LIGHT NUCLEI
MAGNETIC RESONANCE
MOLYBDENUM COMPOUNDS
NUCLEI
ORGANIC COMPOUNDS
ORGANIC HALOGEN COMPOUNDS
OXIDOREDUCTASES
OXYGEN COMPOUNDS
OXYGEN ISOTOPES
REFRACTORY METAL COMPOUNDS
RESONANCE
SPECTRA
STABLE ISOTOPES
TRANSITION ELEMENT COMPOUNDS
VANADIUM COMPOUNDS
550201* - Biochemistry- Tracer Techniques