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2.7.7.74

Accepted name:

1L-myo-inositol 1-phosphate cytidylyltransferase

Reaction:

CTP + 1L-myo-inositol 1-phosphate = diphosphate + CDP-1L-myo-inositol

For diagram of bis(1L-myo-inositol) 1,3′-phosphate biosynthesis, click here

Glossary:

1L-myo-inositol 1-phosphate = 1D-myo-inositol 3-phosphate

Other name(s):

CTP:inositol-1-phosphate cytidylyltransferase (bifunctional CTP:inositol-1-phosphate cytidylyltransferase/CDP-inositol:inositol-1-phosphate transferase (IPCT/DIPPS)); IPCT (bifunctional CTP:inositol-1-phosphate cytidylyltransferase/CDP-inositol:inositol-1-phosphate transferase (IPCT/DIPPS)); L-myo-inositol-1-phosphate cytidylyltransferase

Systematic name:

CTP:1L-myo-inositol 1-phosphate cytidylyltransferase

Comments:

In many organisms this activity is catalysed by a bifunctional enzyme. The cytidylyltransferase domain of the bifunctional EC 2.7.7.74/EC 2.7.8.34 (CTP:inositol-1-phosphate cytidylyltransferase/CDP-inositol:inositol-1-phosphate transferase) is absolutely specific for CTP and 1L-myo-inositol 1-phosphate. The enzyme is involved in biosynthesis of bis(1L-myo-inositol) 1,3′-phosphate, a widespread organic solute in microorganisms adapted to hot environments.

Links to other databases:

BRENDA, EXPASY, KEGG, MetaCyc, PDB

References:

Rodrigues, M.V., Borges, N., Henriques, M., Lamosa, P., Ventura, R., Fernandes, C., Empadinhas, N., Maycock, C., da Costa, M.S. and Santos, H. Bifunctional CTP:inositol-1-phosphate cytidylyltransferase/CDP-inositol:inositol-1-phosphate transferase, the key enzyme for di-myo-inositol-phosphate synthesis in several (hyper)thermophiles. J. Bacteriol. 189 (2007) 5405–5412. [DOI] [PMID: 17526717]

[EC 2.7.7.74 created 2011]

2.7.8.34

Accepted name:

CDP-L-myo-inositol myo-inositolphosphotransferase

Reaction:

CDP-1L-myo-inositol + 1L-myo-inositol 1-phosphate = CMP + bis(1L-myo-inositol) 3,1′-phosphate 1-phosphate

For diagram of bis(1L-myo-inositol) 1,3′-phosphate biosynthesis, click here

Glossary:

1L-myo-inositol 1-phosphate = 1D-myo-inositol 3-phosphate

Other name(s):

CDP-inositol:inositol-1-phosphate transferase (bifunctional CTP:inositol-1-phosphate cytidylyltransferase/CDP-inositol:inositol-1-phosphate transferase (IPCT/DIPPS)); DIPPS (bifunctional CTP:inositol-1-phosphate cytidylyltransferase/CDP-inositol:inositol-1-phosphate transferase (IPCT/DIPPS))

Systematic name:

CDP-1L-myo-inositol:1L-myo-inositol 1-phosphate myo-inositolphosphotransferase

Comments:

In many organisms this activity is catalysed by a bifunctional enzyme. The di-myo-inositol-1,3′-phosphate-1′-phosphate synthase domain of the bifunctional EC 2.7.7.74/EC 2.7.8.34 (CTP:inositol-1-phosphate cytidylyltransferase/CDP-inositol:inositol-1-phosphate transferase) uses only 1L-myo-inositol 1-phosphate as an alcohol acceptor, but CDP-glycerol, as well as CDP-1L-myo-inositol and CDP-D-myo-inositol, are recognized as alcohol donors. The enzyme is involved in biosynthesis of bis(1L-myo-inositol) 1,3-phosphate, a widespread organic solute in microorganisms adapted to hot environments.

Links to other databases:

BRENDA, EXPASY, KEGG, MetaCyc, PDB

References:

[EC 2.7.8.34 created 2011]

2.7.8.39

Accepted name:

archaetidylinositol phosphate synthase

Reaction:

CDP-2,3-bis-(O-phytanyl)-sn-glycerol + 1L-myo-inositol 1-phosphate = CMP + 1-archaetidyl-1D-myo-inositol 3-phosphate

Glossary:

1L-myo-inositol 1-phosphate = 1D-myo-inositol 3-phosphate
CDP-2,3-bis-(O-phytanyl)-sn-glycerol = CDP-2,3-di-(O-phytanyl)-sn-glycerol = CDP-archaeol
1-archaetidyl-1D-myo-inositol 3-phosphate = archaetidyl-myo-inositol 1-phosphate

Other name(s):

AIP synthase

Systematic name:

CDP-2,3-bis-(O-phytanyl)-sn-glycerol:1L-myo-inositol 1-phosphate 1-sn-archaetidyltransferase

Comments:

Requires Mg²⁺ or Mn²⁺ for activity. The enzyme is involved in biosynthesis of archaetidyl-myo-inositol, a compound essential for glycolipid biosynthesis in archaea.

Links to other databases:

BRENDA, EXPASY, KEGG, MetaCyc

References:

Morii, H., Kiyonari, S., Ishino, Y. and Koga, Y. A novel biosynthetic pathway of archaetidyl-myo-inositol via archaetidyl-myo-inositol phosphate from CDP-archaeol and D-glucose 6-phosphate in methanoarchaeon Methanothermobacter thermautotrophicus cells. J. Biol. Chem. 284 (2009) 30766–30774. [DOI] [PMID: 19740749]

[EC 2.7.8.39 created 2013]

5.5.1.4

Accepted name:

inositol-3-phosphate synthase

Reaction:

D-glucose 6-phosphate = 1D-myo-inositol 3-phosphate

For diagram of myo-inositol biosynthesis, click here and for mechanism of reaction, click here

Other name(s):

myo-inositol-1-phosphate synthase; D-glucose 6-phosphate cycloaldolase; inositol 1-phosphate synthatase; glucose 6-phosphate cyclase; inositol 1-phosphate synthetase; glucose-6-phosphate inositol monophosphate cycloaldolase; glucocycloaldolase; 1L-myo-inositol-1-phosphate lyase (isomerizing)

Systematic name:

1D-myo-inositol-3-phosphate lyase (isomerizing)

Comments:

Requires NAD⁺, which dehydrogenates the -CHOH- group to -CO- at C-5 of the glucose 6-phosphate, making C-6 into an active methylene, able to condense with the -CHO at C-1. Finally, the enzyme-bound NADH reconverts C-5 into the -CHOH- form.

Links to other databases:

BRENDA, EXPASY, KEGG, MetaCyc, PDB, CAS registry number: 9032-95-5

References:

1.	Eisenberg, F., Jr. D-Myoinositol 1-phosphate as product of cyclization of glucose 6-phosphate and substrate for a specific phosphatase in rat testis. J. Biol. Chem. 242 (1967) 1375–1382. [PMID: 4290245]
2.	Sherman, W.R., Stewart, M.A. and Zinbo, M. Mass spectrometric study on the mechanism of D-glucose 6-phosphate-L-myo-inositol 1-phosphate cyclase. J. Biol. Chem. 244 (1969) 5703–5708. [PMID: 4310603]
3.	Barnett, J.E.G. and Corina, D.L. The mechanism of glucose 6-phosphate-D-myo-inositol 1-phosphate cyclase of rat testis. The involvement of hydrogen atoms. Biochem. J. 108 (1968) 125–129. [PMID: 4297937]
4.	Barnett, J.E.G., Rasheed, A. and Corina, D.L. Partial reactions of glucose 6-phosphate-1L-myo-inositol 1-phosphate cyclase. Biochem. J. 131 (1973) 21–30. [PMID: 4352864]

[EC 5.5.1.4 created 1972, modified 2001]