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Methylococcus capsulatus (Bath) was grown in continuous culture with methanol (1·0%, v/v) as sole carbon and energy source. Cells grown on methanol exhibited differences in methane monooxygenase (MMO) activity which were dependent on the concentration of copper sulphate present in the growth medium; an increase in the concentration of copper in the growth medium enhanced both in vivo and in vitro MMO activity. The MMO activity in methanol-grown Methylococcus capsulatus (Bath) was always associated with the particulate fraction of cell-free extracts; at no time was soluble MMO activity detected. In vitro MMO activity was also stimulated by the addition of copper compounds to the assay system and the stimulation was shown to be pH-dependent. The concentration of copper sulphate in the growth medium also determined the intracytoplasmic membrane content of the cells, as judged by electron microscopy of thin-sections, which could be correlated with particulate MMO activity, although it is not possible at this time to say whether the increase in MMO activity seen is due to the increased membrane content or due to the copper ions per se.
Prior et al. (Tue,) studied this question.