14N‐coordination to VO2+ in reduced vanadium bromoperoxidase, an electron spin echo study

Abstract

Vanadium bromoperoxidase from the brown seaweed Ascophyllum nodosum was studied with electron spin echo envelope modulation (ESEEM) spectroscopy. After comparing the Fourier transformed (FT) ESEEM spectra with those of a number of vanadyl model compounds, it could be concluded that nitrogen is present in the equatorial plane of the vanadyl cation of reduced bromoperoxidase (¹⁴N frequencies occurred at 3.1, 4.2, 5.3 and 8.1 MHz). Furthermore, the FT‐ESEEM spectra of reduced bromoperoxidase exhibited an intense ¹H modulation (13.8 MHz), which was completely replaced by a deuterium modulation at ∼2 MHz when bromoperoxidase was dissolved in D₂O, instead of H₂O. These latter data confirm earlier EPR experiments on reduced bromoperoxidase [(1988) Biochemistry 27, 1629–1635], showing that the oxo‐vanadium (IV) ion is coupled to exchangeable protons.