Membrane-associated quinoprotein formaldehyde dehydrogenase from Methylococcus capsulatus Bath

Area of Science:

• Biochemistry
• Microbiology
• Enzymology

Background:

• Methylococcus capsulatus Bath utilizes methane as a carbon and energy source.
• Copper availability influences the expression of methane monooxygenases and formaldehyde oxidation pathways in this organism.
• Previous studies indicated soluble formaldehyde oxidation pathways under low copper conditions.

Purpose of the Study:

• To isolate and characterize the membrane-associated formaldehyde dehydrogenase (DL-FalDH) from Methylococcus capsulatus Bath.
• To determine the cofactor and electron acceptor of the DL-FalDH.
• To understand the role of DL-FalDH in formaldehyde metabolism under specific growth conditions.

Main Methods:

• Enzyme isolation and purification from Methylococcus capsulatus Bath.
• Spectroscopic techniques (UV-visible absorption, EPR) for cofactor identification.
• Mass spectrometry for molecular mass determination and stoichiometry.
• Enzyme activity assays with formaldehyde and potential electron acceptors.

Main Results:

• A membrane-associated DL-FalDH was isolated, predominantly expressed in high copper medium with membrane-associated methane monooxygenase.
• The enzyme is a homotetramer with a subunit molecular mass of 49,500 Da.
• Spectroscopic and mass spectrometry data indicate pyrroloquinoline quinone (PQQ) as the redox cofactor with a 1:1 stoichiometry.
• DL-FalDH specifically oxidized formaldehyde to formate, using the cytochrome b(559/569) complex as the electron acceptor.

Conclusions:

• DL-FalDH is a significant formaldehyde-oxidizing enzyme in Methylococcus capsulatus Bath under conditions favoring membrane-bound methane oxidation.
• Pyrroloquinoline quinone (PQQ) is the redox cofactor for this membrane-associated enzyme.
• The cytochrome b(559/569) complex serves as the physiological electron acceptor for DL-FalDH.