Trimethylamine-N-oxide reductase (cytochrome c)
Trimethylamine-N-oxide reductase (cytochrome c), also known as TMAO reductase (cytochrome c), is an enzyme that catalyzes the reduction of trimethylamine N-oxide (TMAO) to trimethylamine (TMA) using a cytochrome c molecule as an electron donor. This enzyme plays a crucial role in anaerobic respiration in various bacteria, particularly those found in marine environments and the gut.
The reaction catalyzed by trimethylamine-N-oxide reductase (cytochrome c) is as follows:
Trimethylamine N-oxide + 2 H+ + 2 e- → Trimethylamine + H2O
The enzyme is typically a molybdenum-containing enzyme, where molybdenum acts as the catalytic center for the reduction of TMAO. It is anchored to the periplasmic face of the cytoplasmic membrane, allowing it to interact with both TMAO in the periplasm and cytochrome c in the membrane.
Functionally, the reduction of TMAO by this enzyme allows bacteria to use TMAO as a terminal electron acceptor in anaerobic environments, similar to the way that oxygen is used in aerobic respiration. This allows these organisms to generate energy (ATP) in the absence of oxygen, contributing significantly to their survival and ecological roles in environments such as marine sediments and the gastrointestinal tract of animals.
The enzyme is important in the context of dimethyl sulfide (DMS) production as TMAO, produced from degradation of compounds like choline and betaine, is reduced to TMA. TMA can then be metabolized to DMS, contributing to the global sulfur cycle.
Studies have also shown the activity of TMAO reductase (cytochrome c) and the resulting TMA production by gut bacteria to be associated with cardiovascular diseases in humans, making it a subject of ongoing research.