<Li> Urinary γ - carboxyglutamic acid responds to changes in dietary vitamin K intake . Several days are required before any change can be observed . In a study by Booth et al., increases of phylloquinone intakes from 100 μg to between 377 and 417 μg for five days did not induce a significant change . Response may be age - specific . </Li> <Li> Undercarboxylated osteocalcin (UcOc) levels have been inversely correlated with stores of vitamin K and bone strength in developing rat tibiae . Another study following 78 post-menopausal Korean women found a supplement regimen of vitamins K and D, and calcium, but not a regimen of vitamin D and calcium, was inversely correlated with reduced UcOc levels . </Li> <P> Many bacteria, such as Escherichia coli found in the large intestine, can synthesize vitamin K (menaquinone - 7 or MK - 7, up to MK - 11), but not vitamin K (phylloquinone). In these bacteria, menaquinone transfers two electrons between two different small molecules, during oxygen - independent metabolic energy production processes (anaerobic respiration). For example, a small molecule with an excess of electrons (also called an electron donor) such as 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 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 . </P> <P> Some of these reactions generate a cellular energy source, 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 (O), which accepts four electrons from an electron donor such as NADH to be converted to water . E. coli, as facultative anaerobes, can carry out both aerobic respiration and menaquinone - mediated anaerobic respiration . </P>

In large intestine vitamin k is formed by the activity of which bacteria