Linked Life Data

11153266

Source:http://linkedlifedata.com/resource/pubmed/id/11153266

Statements in which the resource exists as a subject.
PredicateObject
rdf:type
lifeskim:mentions
pubmed:dateCreated
2001-1-10
pubmed:abstractText
The benzoquinone ubiquinone (coenzyme Q) and the naphthoquinones menaquinone (vitamin K2) and demethylmenaquinone are derived from the shikimate pathway, which has been described as a "metabolic tree with many branches." Menaquinone (MK) is considered a vitamin, but coenzyme (Q) is not; MK is an essential nutrient (it cannot be synthesized by mammals), whereas Q is not considered an essential nutrient since it can be synthesized from the amino acid tyrosine. The quinone nucleus of Q is derived directly from chorismate, whereas that of MK is derived from chorismate via isochorismate. The prenyl side chain of both quinones is derived from prenyl diphosphate, and the methyl groups are derived from S-adenosylmethionine. MK biosynthesis requires 2-ketoglutarate and the cofactors ATP, coenzyme A (CoASH), and thiamine pyrophosphate. In spite of the fact that both quinones originate from the shikimate pathway, there are important differences in their biosynthesis. In MK biosynthesis, the prenyl side chain is introduced in the next to last step, which is accompanied by loss of the carboxyl group, whereas in Q biosynthesis, the prenyl side chain is introduced at the second step, with retention of the carboxyl group. In MK biosynthesis, all the reactions of the pathway up to the prenylation (next to last step) are carried out by soluble enzymes, whereas all the enzymes involved in Q biosynthesis except the first are membrane bound. In MK biosynthesis the last step is a C-methylation; in Q biosynthesis, the last step is an O-methylation. In Q biosynthesis a second C-methylation and O-methylation take place in the middle part of the pathway. In spite of the fact that Q and MK biosynthesis diverges at chorismate, the C-methylations involved in both pathways are carried out by the same enzyme. Finally, Q biosynthesis under aerobic conditions requires molecular oxygen; anaerobic biosynthesis of Q and MK incorporates oxygen atoms derived from water. The current status of the pathways with particular emphasis on the reaction mechanisms, is discussed in this review.
pubmed:grant
pubmed:language
eng
pubmed:journal
pubmed:citationSubset
IM
pubmed:chemical
pubmed:status
MEDLINE
pubmed:issn
0083-6729
pubmed:author
pubmed:issnType
Print
pubmed:volume
61
pubmed:owner
NLM
pubmed:authorsComplete
Y
pubmed:pagination
173-218
pubmed:dateRevised
2007-11-14
pubmed:meshHeading
pubmed:year
2001
pubmed:articleTitle
Biosynthesis of menaquinone (vitamin K2) and ubiquinone (coenzyme Q): a perspective on enzymatic mechanisms.
pubmed:affiliation
Department of Biological Sciences, Northern Illinois University, DeKalb, Illinois 60115, USA.
pubmed:publicationType
Journal Article, Research Support, U.S. Gov't, P.H.S., Review