Molecular biology and regulation of methane monooxygenase

Methanotrophs are ubiquitous in the environment and play an important role in mitigating global warming due to methane. They are also potentially inte resting for industrial applications such as production of bulk chemicals or bioremediation. The first step in the oxidation of methane is the conversi on to methanol by methane monooxygenase, the key enzyme, which exists in tw o forms: the cytoplasmic, soluble methane monooxygenase (sMMO) and the memb rane-bound, particulate methane monooxygenase (pMMO). This paper reviews th e biochemistry and molecular biology of both forms of MMO. In the past few years there have been many exciting new findings. sMMO components have been expressed in heterologous and homologous hosts. The pMMO has been purified and biochemically studied in some detail and the genes encoding the pMMO h ave been sequenced. Copper ions have been shown to play a key role in regul ating the expression of both MMO enzyme complexes. We also present a model for copper regulation based on results from Northern analysis, primer-exten sions and new sequence data, and raise a number of unanswered questions for future studies.