The metal centres of particulate methane mono-oxygenase.
- Amy C Rosenzweig
- Biochemical Society transactions
All methanotrophic bacteria express a membrane-bound (particulate) methane mono-oxygenase (pMMO). In the present study, we have investigated pMMO in membrane fragments from Methylococcus capsulatus (strain M). pMMO contains a typical type-2 Cu#+ centre with the following EPR parameters : g z 2.24, g x,y 2.06, ACu z 19.0 mT and ACu x,y 1.0 mT. Simulation of the Cu#+ spectrum yielded a best match by using four equivalent nitrogens (AN ̄ 1.5 mT, 42 MHz). Incubation with ferricyanide neither changed nor increased the amount of EPR-active Cu#+, in contrast with other reports. The EPR visible copper seems not to be part of any cluster, as judged from the microwave power saturation behaviour. Continuous-wave electron–nuclear double resonance (CW ENDOR; 9.4 GHz, 5–20 K) experiments at gv of the Cu(II) spectrum show a weak coupling to protons with an AH of 2.9 MHz that corresponds to a distance of 3.8 AI (1 AI 3 0.1 nm), assuming that it is a purely dipolar coupling. Incubation in #H # O leads to a significant decrease in these "HENDOR intensities, showing that these protons are exchangeable. This result strongly suggests that the EPR visible copper