EPR, electron spin echo envelope modulation, and electron nuclear double resonance studies of the 2Fe2S centers of the 2-halobenzoate 1,2-dioxygenase from Burkholderia (Pseudomonas) cepacia 2CBS

The 2-halobenzoate 1,2-dioxygenase from Burkholderia (Pseudomonas) cepacia 2CBS (Fetzner, S., Muller, R., and Lingens, F. (1992) J. Bacteriol. 174, 279- 290) contains both a ferredoxin-type and a Rieske-type 2Fe2S center. These two significantly different 2Fe2S clusters were characterized with respect to their EPR spectra, electrochemical properties (Rieske-type cluster with g(z) = 2.025, g(y) = 1.91, g(x) = 1.79, g(av) = 1.91, E(m) = -125 ± 10 mV; ferredoxin-type center with g(z) = 2.05, g(y) = 1.96, g(x) = 1.89, g(av) = 1.97, E(m) = -200 ± 10 mV) and pH dependence thereof. X band electron spin echo envelope modulation and electron nuclear double resonance spectroscopy was applied to study the interaction of the Rieske-type center of the 2- halobenzoate 1,2-dioxygenase with ¹⁴N and ¹H nuclei in the vicinity of the 2Fe2S cluster. The results are compared to those obtained on the Rieske protein of the cytochrome b₆f complex (E(m) = +320 mV) and the water- soluble ferredoxin (E(m) = -430 mV) of spinach chloroplasts, as typical representatives of the g(av)=1.91 and g(av) = 1.96 class of 2Fe2S centers. Properties common to all Rieske-type clusters and those restricted to the respective centers in bacterial oxygenases are discussed.