Methane
Mammalian methanogenesis is widely considered to be an exclusive sign of anaerobic microbial activity in the gastrointestinal tract. Methanogenesis in microbes is a form of anaerob condition.
CO2 + 4 H2 → CH4 + 2H2O
CH3COOH → CH4 + CO2
Methane has previously been considered an inactive gas that is mainly excreted in flatus, while a certain amount is excreted in breath. However, recently, methane has been associated with gastrointestinal disorders, mainly chronic constipation and constipation predominant irritable bowel syndrome (IBS), as well as metabolic diseases like obesity. Exogenously inhaled methane moves from the alveoli into the circulation, diffusing into the plasma, throughout which it is distributes rapidly and evenly. The solubility of methane in blood is rather low but the solubility in membrane bilayers is significantly higher. Ghyczy et al. demonstrated aerobic methane emission in cultured endothelial cells exposed to hypoxia and metabolic distress. The disturbance of the normal mitochondrial function leads to significant methane generation in endothelial cells, depending on the nature and intensity of the metabolic distress. The rearrangement of the electron transport results in an elevated production of ROS. As in plants, the release of methane may be associated with ROS generation after transient intracellular O2 deprivation and may be an integral feature of cellular responses to changes in oxidative status in all eukaryotes.