Comparison of EPR-Visible Cu2+ Sites in pMMO from Methylococcus capsulatus (Bath) and Methylomicrobium album BG8

AbstractX-band (9.1GHz) and S-band (3.4GHz) electron paramagnetic resonance (EPR) spectra for particulate methane monooxygenase (pMMO) in whole cells from Methylococcus capsulatus (Bath) grown on 63Cu and 15N were obtained and compared with previously reported spectra for pMMO from Methylomicrobium album BG8. For both M. capsulatus (Bath) and M. album BG8, two nearly identical Cu2+ EPR signals with resolved hyperfine coupling to four nitrogens are observed. The EPR parameters for pMMO from M. capsulatus (Bath) (g||=2.244, A||=185 G, and AN=19G for signal one; g||=2.246, A||=180 G, and AN=19G for signal two) and for pMMO from M. album BG8 (g||=2.243, A||=180 G, and AN=18G for signal one; g||=2.251, A||=180 G, and AN=18G for signal two) are very similar and are characteristic of type 2 Cu2+ in a square planar or square pyramidal geometry. In three-pulse electron spin echo envelope modulation (ESEEM) data for natural-abundance samples, nitrogen quadrupolar frequencies due to the distant nitrogens of coordinated histidine imidazoles were observed. The intensities of the quadrupolar combination bands indicate that there are three or four coordinated imidazoles, which implies that most, if not all, of the coordinated nitrogens detected in the continuous wave spectra are from histidine imidazoles