Editing Vitamin K (section)

=== Function in other bacteria ===
Many bacteria, including ''[[Escherichia coli]]'' found in the [[large intestine]], can synthesize vitamin K<sub>2</sub> (MK-7 up to MK-11),<ref name=Bentley>{{cite journal | vauthors = Bentley R, Meganathan R | title = Biosynthesis of vitamin K (menaquinone) in bacteria | journal = Microbiological Reviews | volume = 46 | issue = 3 | pages = 241–280 | date = September 1982 | pmid = 6127606 | pmc = 281544 | doi = 10.1128/MMBR.46.3.241-280.1982 }}</ref> but not vitamin K<sub>1</sub>. In the vitamin K<sub>2</sub> synthesizing bacteria, menaquinone transfers two [[electron]]s between two different small molecules, during oxygen-independent metabolic energy production processes ([[anaerobic respiration]]).<ref name=Haddock>{{cite journal | vauthors = Haddock BA, Jones CW | title = Bacterial respiration | journal = Bacteriological Reviews | volume = 41 | issue = 1 | pages = 47–99 | date = March 1977 | pmid = 140652 | pmc = 413996 | doi = 10.1128/mmbr.41.1.47-99.1977 }}</ref> For example, a small molecule with an excess of electrons (also called an electron donor) such as [[lactic acid|lactate]], [[formate]], or [[NADH]], with the help of an enzyme, passes two electrons to menaquinone. The menaquinone, with the help of another enzyme, then transfers these two electrons to a suitable oxidant, such as [[fumarate]] or [[nitrate]] (also called an electron acceptor). Adding two electrons to [[fumarate]] or [[nitrate]] converts the molecule to [[succinate]] or [[nitrite]] plus [[water]], respectively.<ref name=Haddock /> 

Some of these reactions generate a cellular energy source, [[adenosine triphosphate|ATP]], in a manner similar to [[eukaryotic]] cell [[aerobic respiration]], except the final electron acceptor is not [[molecular oxygen]], but [[fumarate]] or [[nitrate]]. In [[aerobic respiration]], the final oxidant is [[molecular oxygen]], which accepts four electrons from an electron donor such as [[NADH]] to be converted to [[water]]. ''E. coli'', as [[facultative anaerobe]]s, can carry out both [[aerobic respiration]] and menaquinone-mediated anaerobic respiration.<ref name=Haddock />