Applications of Enzyme Biotechnology

Part of the series Industry-University Cooperative Chemistry Program Symposia pp 69-85

Studies of Methane Monooxygenase and Alkane Oxidation Model Complexes

  • Amy C. RosenzweigAffiliated withDepartment of Chemistry, Massachusetts Institute of Technology
  • , Xudong FengAffiliated withDepartment of Chemistry, Massachusetts Institute of Technology
  • , Stephen J. LippardAffiliated withDepartment of Chemistry, Massachusetts Institute of Technology

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Among the recently delineated class of non-heme iron oxo proteins is the hydroxylase component of methane monooxygenase, an enzyme that catalyzes the conversion of methane to methanol according to eq. 1.1 Methane monooxygenases (MMOs) are found in methanotrophic bacteria
$$ C{H_4} + NADH + {H^ + } + {O_2} \to C{H_3}OH + NA{D^ + } + {H_2}O $$
that use methane as their sole source of carbon and energy.2 In this article we discuss mainly the results of studies that have been carried out on MMOs from the organisms Methylococcus capsulatus (Bath) and Methylosinus trichosporium OB3b. The soluble MMOs from both of these organisms contain two proteins in addition to the hydroxylase, a reductase with associated FAD and Fe2S2 prosthetic groups and a smaller polypeptide, designated protein B, that is believed to play a role in regulating electron transfer between the reductase and hydroxylase components.3, 4 The relative roles of these proteins in the overall MMO system are displayed in Figure 1. Most catalysts that effect the hydroxylation of alkanes by dioxygen are also able to catalyze the direct oxidation (autoxidation) of the reductant with dioxygen. The MMO system avoids this potential problem by physically isolating the hydroxylase and reductase functionalities on different proteins.