Accepted name: 4-hydroxysphinganine ceramide fatty acyl 2-hydroxylase
Reaction: a phytoceramide + 2 ferrocytochrome b5 + O2 + 2 H+ = a (2′R)-2′-hydroxyphytoceramide + 2 ferricytochrome b5 + H2O
Glossary: a phytoceramide = a (4R)-4-hydroxysphinganine ceramide = an N-acyl-4-hydroxysphinganine
Other name(s): FA2H (gene name); SCS7 (gene name)
Systematic name: (4R)-4-hydroxysphinganine ceramide,ferrocytochrome-b5:oxygen oxidoreductase (fatty acyl 2-hydroxylating)
Comments: The enzyme, characterized from yeast and mammals, catalyses the hydroxylation of carbon 2 of long- or very-long-chain fatty acids attached to (4R)-4-hydroxysphinganine during de novo ceramide synthesis. The enzymes from yeast and from mammals contain an N-terminal cytochrome b5 domain that acts as the direct electron donor to the desaturase active site. The newly introduced 2-hydroxyl group has R-configuration. cf. EC, dihydroceramide fatty acyl 2-hydroxylase.
1.  Mitchell, A.G. and Martin, C.E. Fah1p, a Saccharomyces cerevisiae cytochrome b5 fusion protein, and its Arabidopsis thaliana homolog that lacks the cytochrome b5 domain both function in the α-hydroxylation of sphingolipid-associated very long chain fatty acids. J. Biol. Chem. 272 (1997) 28281–28288. [PMID: 9353282]
2.  Dunn, T.M., Haak, D., Monaghan, E. and Beeler, T.J. Synthesis of monohydroxylated inositolphosphorylceramide (IPC-C) in Saccharomyces cerevisiae requires Scs7p, a protein with both a cytochrome b5-like domain and a hydroxylase/desaturase domain. Yeast 14 (1998) 311–321. [PMID: 9559540]
3.  Alderson, N.L., Rembiesa, B.M., Walla, M.D., Bielawska, A., Bielawski, J. and Hama, H. The human FA2H gene encodes a fatty acid 2-hydroxylase. J. Biol. Chem. 279 (2004) 48562–48568. [PMID: 15337768]
4.  Eckhardt, M., Yaghootfam, A., Fewou, S.N., Zoller, I. and Gieselmann, V. A mammalian fatty acid hydroxylase responsible for the formation of α-hydroxylated galactosylceramide in myelin. Biochem. J. 388 (2005) 245–254. [PMID: 15658937]
5.  Guo, L., Zhang, X., Zhou, D., Okunade, A.L. and Su, X. Stereospecificity of fatty acid 2-hydroxylase and differential functions of 2-hydroxy fatty acid enantiomers. J. Lipid Res. 53 (2012) 1327–1335. [PMID: 22517924]
[EC created 2015]
Accepted name: sphingolipid 8-(E/Z)-desaturase
Reaction: (1) a (4R)-4-hydroxysphinganine ceramide + 2 ferrocytochrome b5 + O2 + 2 H+ = a (4R,8E)-4-hydroxysphing-8-enine ceramide + 2 ferricytochrome b5 + 2 H2O
(2) a (4R)-4-hydroxysphinganine ceramide + 2 ferrocytochrome b5 + O2 + 2 H+ = a (4R,8Z)-4-hydroxysphing-8-enine ceramide + 2 ferricytochrome b5 + 2 H2O
Glossary: a (4R)-4-hydroxysphinganine-ceramide = a phytoceramide
(4R)-4-hydroxysphinganine = phytosphinganine
Other name(s): 8-sphingolipid desaturase (ambiguous); 8 fatty acid desaturase (ambiguous); DELTA8-sphingolipid desaturase (ambiguous)
Systematic name: (4R)-4-hydroxysphinganine ceramide,ferrocytochrome b5:oxygen oxidoreductase (8,9 cis/trans-dehydrogenating)
Comments: The enzymes from higher plants convert sphinganine, 4E-sphing-4-enine and phytosphinganine into E/Z-mixtures of Δ8-desaturated products displaying different proportions of geometrical isomers depending on plant species. The nature of the actual desaturase substrate has not yet been studied experimentally. The enzymes contain an N-terminal cytochrome b5 domain that acts as the direct electron donor to the active site of the desaturase [1]. The homologous enzymes from some yeasts and diatoms, EC, sphingolipid 8-(E)-desaturase, act on sphing-4-enine ceramides and produce only the trans isomer.
1.  Sperling, P., Zähringer, U. and Heinz, E. A sphingolipid desaturase from higher plants. Identification of a new cytochrome b5 fusion protein. J. Biol. Chem. 273 (1998) 28590–28596. [PMID: 9786850]
2.  Sperling, P., Blume, A., Zähringer, U., and Heinz, E. Further characterization of Δ8-sphingolipid desaturases from higher plants. Biochem Soc Trans. 28 (2000) 638–641. [PMID: 11171153]
3.  Sperling, P., Libisch, B., Zähringer, U., Napier, J.A. and Heinz, E. Functional identification of a Δ8-sphingolipid desaturase from Borago officinalis. Arch. Biochem. Biophys. 388 (2001) 293–298. [PMID: 11368168]
4.  Beckmann, C., Rattke, J., Oldham, N.J., Sperling, P., Heinz, E. and Boland, W. Characterization of a Δ8-sphingolipid desaturase from higher plants: a stereochemical and mechanistic study on the origin of E,Z isomers. Angew. Chem. Int. Ed. Engl. 41 (2002) 2298–2300. [PMID: 12203571]
5.  Ryan, P.R., Liu, Q., Sperling, P., Dong, B., Franke, S. and Delhaize, E. A higher plant Δ8 sphingolipid desaturase with a preference for (Z)-isomer formation confers aluminum tolerance to yeast and plants. Plant Physiol. 144 (2007) 1968–1977. [PMID: 17600137]
6.  Chen, M., Markham, J.E. and Cahoon, E.B. Sphingolipid Δ8 unsaturation is important for glucosylceramide biosynthesis and low-temperature performance in Arabidopsis. Plant J. 69 (2012) 769–781. [PMID: 22023480]
[EC created 2015]
Accepted name: inositol phosphorylceramide mannosyltransferase
Reaction: GDP-α-D-mannose + a (4R)-4-hydroxy-N-[(2R)-2-hydroxy-very-long-chain-acyl]-1-O-[(1D-myo-inositol-1-O-yl)hydroxyphosphoryl]sphinganine = a (4R)-4-hydroxy-N-[(2R)-2-hydroxy-very-long-chain-acyl]-1-O-{[6-O-(α-D-mannosyl)-1D-myo-inositol-1-O-yl]hydroxyphosphoryl}sphinganine + GDP
Glossary: a (4R)-4-hydroxy-N-[(2R)-2-hydroxy-very-long-chain-acyl]-1-O-[(1D-myo-inositol-1-O-yl)hydroxyphosphoryl]sphinganine = a very-long-chain inositol phospho-α hydroxyphytoceramide = IPC
a (4R)-4-hydroxy-N-[(2R)-2-hydroxy-very-long-chain-acyl]-1-O-{[6-O-(α-D-mannosyl)-1D-myo-inositol-1-O-yl]hydroxyphosphoryl}sphinganine = a very-long-chain mannosylinositol phospho-α-hydroxyphytoceramide = MIPC
Other name(s): SUR1 (gene name); CSH1 (gene name)
Systematic name: GDP-α-D-mannose:(4R)-4-hydroxy-N-[(2R)-2-hydroxy-very-long-chain-acyl]-1-O-[(1D-myo-inositol-1-O-yl)hydroxyphosphoryl]sphinganine mannosyltransferase (configuration-retaining)
Comments: The simplest complex sphingolipid of yeast, inositol-phospho-α-hydroxyphytoceramide (IPC), is usually mannosylated to yield mannosyl-inositol-phospho-α hydroxyphytoceramide (MIPC). The enzyme is located in the Golgi apparatus, and utilizes GDP-mannose as the mannosyl group donor. It consists of a catalytic subunit (SUR1 or CSH1) and a regulatory subunit (CSG2).
1.  Beeler, T.J., Fu, D., Rivera, J., Monaghan, E., Gable, K. and Dunn, T.M. SUR1 (CSG1/BCL21), a gene necessary for growth of Saccharomyces cerevisiae in the presence of high Ca2+ concentrations at 37 degrees C, is required for mannosylation of inositolphosphorylceramide. Mol. Gen. Genet. 255 (1997) 570–579. [PMID: 9323360]
2.  Dean, N., Zhang, Y.B. and Poster, J.B. The VRG4 gene is required for GDP-mannose transport into the lumen of the Golgi in the yeast, Saccharomyces cerevisiae. J. Biol. Chem. 272 (1997) 31908–31914. [PMID: 9395539]
3.  Uemura, S., Kihara, A., Inokuchi, J. and Igarashi, Y. Csg1p and newly identified Csh1p function in mannosylinositol phosphorylceramide synthesis by interacting with Csg2p. J. Biol. Chem. 278 (2003) 45049–45055. [PMID: 12954640]
[EC created 2019]
Accepted name: inositol phosphorylceramide synthase
Reaction: 1-phosphatidyl-1D-myo-inositol + a very-long-chain (2′R)-2′-hydroxy-phytoceramide = 1,2-diacyl-sn-glycerol + a (4R)-4-hydroxy-N-[(2R)-2-hydroxy-very-long-chain-acyl]-1-O-[(1D-myo-inositol-1-O-yl)hydroxyphosphoryl]sphinganine
Glossary: a (4R)-4-hydroxy-N-[(2R)-2-hydroxy-very-long-chain-acyl]-1-O-[(1D-myo-inositol-1-O-yl)hydroxyphosphoryl]sphinganine = a very-long-chain inositol phospho-α hydroxyphytoceramide = IPC
Other name(s): AUR1 (gene name); KEI1 (gene name)
Systematic name: 1-phosphatidyl-1D-myo-inositol:a very-long-chain (2′R)-2′-hydroxy-phytoceramide phosphoinositoltransferase
Comments: The enzyme, characterized from yeast, attaches a phosphoinositol headgroup to α-hydroxyphytoceramides, generating a very-long-chain inositol phospho-α hydroxyphytoceramide (IPC), the simplest of the three complex sphingolipids produced by yeast.
1.  Nagiec, M.M., Nagiec, E.E., Baltisberger, J.A., Wells, G.B., Lester, R.L. and Dickson, R.C. Sphingolipid synthesis as a target for antifungal drugs. Complementation of the inositol phosphorylceramide synthase defect in a mutant strain of Saccharomyces cerevisiae by the AUR1 gene. J. Biol. Chem. 272 (1997) 9809–9817. [PMID: 9092515]
2.  Levine, T.P., Wiggins, C.A. and Munro, S. Inositol phosphorylceramide synthase is located in the Golgi apparatus of Saccharomyces cerevisiae. Mol. Biol. Cell 11 (2000) 2267–2281. [PMID: 10888667]
3.  Sato, K., Noda, Y. and Yoda, K. Kei1: a novel subunit of inositolphosphorylceramide synthase, essential for its enzyme activity and Golgi localization. Mol. Biol. Cell 20 (2009) 4444–4457. [PMID: 19726565]
[EC created 2019]
Accepted name: mannosyl-inositol-phosphoceramide inositolphosphotransferase
Reaction: 1-phosphatidyl-1D-myo-inositol + a (4R)-4-hydroxy-N-[(2R)-2-hydroxy-very-long-chain-acyl]-1-O-{[6-O-(α-D-mannosyl)-1D-myo-inositol-1-O-yl]hydroxyphosphoryl}sphinganine = 1,2-diacyl-sn-glycerol + a (4R)-4-hydroxy-N-[(2R)-2-hydroxy-very-long-chain-acyl]-1-O-[(6-O-{6-O-[(1D-myo-inositol-1-O-yl)hydroxyphosphoryl]-α-D-mannosyl}-1D-myo-inositol-1-O-yl)hydroxyphosphoryl]sphinganine
Glossary: a (4R)-4-hydroxy-N-[(2R)-2-hydroxy-very-long-chain-acyl]-1-O-{[6-O-(α-D-mannosyl)-1D-myo-inositol-1-O-yl]hydroxyphosphoryl}sphinganine = a very-long-chain mannosylinositol phospho-α-hydroxyphytoceramide = MIPC
a (4R)-4-hydroxy-N-[(2R)-2-hydroxy-very-long-chain-acyl]-1-O-[(6-O-{6-O-[(1D-myo-inositol-1-O-yl)hydroxyphosphoryl]-α-D-mannosyl}-1D-myo-inositol-1-O-yl)hydroxyphosphoryl]sphinganine = a very-long-chain mannosyl-diphosphoinositol-α-hydroxyphytoceramide = MIP2C
Other name(s): IPT1 (gene name)
Systematic name: 1-phosphatidyl-1D-myo-inositol:(4R)-4-hydroxy-N-[(2R)-2-hydroxy-very-long-chain-acyl]-1-O-{[6-O-(α-D-mannosyl)-1D-myo-inositol-1-O-yl]hydroxyphosphoryl}sphinganine phosphoinositoltransferase
Comments: This enzyme catalyses the ultimate reaction in the yeast sphingolipid biosynthesis pathway. It transfers a second phosphoinositol group to mannosyl-inositol-phospho-α-hydroxyphytoceramide (MIPC), forming the final and most abundant yeast sphingolipid, mannosyl-diphosphoinositol-ceramide (MIP2C).
1.  Dickson, R.C., Nagiec, E.E., Wells, G.B., Nagiec, M.M. and Lester, R.L. Synthesis of mannose-(inositol-P)2-ceramide, the major sphingolipid in Saccharomyces cerevisiae, requires the IPT1 (YDR072c) gene. J. Biol. Chem. 272 (1997) 29620–29625. [PMID: 9368028]
[EC created 2019]