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= Isochorismate Synthase = Isochorismate synthase (MenF) (EC number 5.4.4.2) is involved in the biosynthesis of vitamin K in Escherichia coli. This enzyme catalyzes the first step in the biosynthesis of menaquinone (vitamin K). [[File:Isochorismate Synthase.png|thumb|Ishochorismate Synthase cartoon view (2 subunits)
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Reaction
Isochorismate synthase is an enzyme that catalyzes the irreversible reaction:

Chorismate→ Isochorismate



The only subrate of this reaction is chorismate, and the product is isochorismate. Isochorismate synthase is most active at 37℃ and at a pH between 7.5-8. Isochorismate synthase requires Mg2+. The concentration of Mg2+ may range from 100μM-1mM. Inhibitors of isochorismate synthase include:
 * (4R,5R)-4-hydroxy-5-(1-carboxyvinyloxy)-cyclohex-1-ene carboxylate
 * (4R,5R)-4-hydroxy-5-carboxymethoxy-cyclohex-1-enecarboxylate
 * (4R,5R)-5-(2-carboxy-allyloxy)-4-hydroxy-cyclohex-1-enecarboxylate
 * (4R,5R,6S)-6-ammonio-5-[(1-carboxylatoethenyl)oxy]-4-hydroxycyclohex-1-ene-1-carboxylate
 * (4R,5R,7R)-5-(1-carboxy-ethoxy)-4-hydroxy-cyclohex-1-enecarboxylate
 * (4R,5R,7S)-5-(1-carboxy-ethoxy)-4-hydroxy-cyclohex-1-enecarboxylate
 * (4R,5S,6S)-4-ammonio-5-[(1-carboxylatoethenyl)oxy]-6-hydroxycyclohex-1-ene-1-carboxylate
 * (4R,5S,6S)-5-[(1-carboxylatoethenyl)oxy]-4,6-dihydroxycyclohex-1-ene-1-carboxylate
 * Cu2+
 * Hg2+
 * K+
 * Mg2+ at concentrations above 1mM
 * NEM

Nomenclature
Isochorismate synthase, or MenF, belongs to the isomerase enzyme family. More specifically it is classified as an intermolecular transferase because it transfers the hydroxy group of chorismate between carbons. The systematic name of this enzyme is isochorismate hydroxymutase, and the common name is isochorismate synthase. Other names for this enzyme include:
 * Isochorismate mutase
 * Menaquinone-specific isochorismate synthase
 * MenF

Vitamin K
Vitamin K is a quinone, which means it is a ring compound that participates in redox reactions. These redox reactions take place in various organisms ranging from plants where electrons are transferred during photosynthesis, humans where electrons are transferred to modify certain types of proteins, and even in bacteria where electrons are transferred during anaerobic respiration.

Pathways
MenF is a gene that codes for the isochorismate synthase found in the menaquinone pathway in Escherichia coli, not to be mistaken for the entC gene that codes for the isochorismate synthase found in the enterobacter pathway in Escherichia coli. Isochorismate synthase has several other homologs that are found in other organisms. These include: