EC 1.14.19.31     
Accepted name: acyl-lipid (7-3)-desaturase
Reaction: (1) a (7Z,10Z,13Z,16Z,19Z)-docosa-7,10,13,16,19-pentaenoyl-[glycerolipid] + 2 ferrocytochrome b5 + O2 + 2 H+ = a (4Z,7Z,10Z,13Z,16Z,19Z)-docosa-4,7,10,13,16,19-hexaenoyl-[glycerolipid] + 2 ferricytochrome b5 + 2 H2O
(2) a (7Z,10Z,13Z,16Z)-docosa-7,10,13,16-tetraenoyl-[glycerolipid] + 2 ferrocytochrome b5 + O2 + 2 H+ = a (4Z,7Z,10Z,13Z,16Z)-docosa-4,7,10,13,16-pentaenoyl-[glycerolipid] + 2 ferricytochrome b5 + 2 H2O
Glossary: (7Z,10Z,13Z,16Z)-docosa-7,10,13,16-tetraenoate = adrenate
Other name(s): D4Des (gene name); des1 (gene name); CrΔ4FAD (gene name); acyl-lipid 4-desaturase
Systematic name: Δ7 acyl-lipid,ferrocytochrome b5:oxygen oxidoreductase (4,5 cis-dehydrogenating)
Comments: The enzymes from several algae introduce a cis double bond at the 4-position in 22-carbon polyunsaturated fatty acids that contain a Δ7 double bond. The enzyme from the fresh water alga Chlamydomonas reinhardtii acts on the 16 carbon fatty acid (7Z,10Z,13Z)-hexadeca-7,10,13-trienoate [5]. The enzyme contains an N-terminal cytochrome b5 domain that acts as the direct electron donor to the active site of the desaturase, and does not require an external cytochrome.
References:
1.  Qiu, X., Hong, H. and MacKenzie, S.L. Identification of a Δ4 fatty acid desaturase from Thraustochytrium sp. involved in the biosynthesis of docosahexanoic acid by heterologous expression in Saccharomyces cerevisiae and Brassica juncea. J. Biol. Chem. 276 (2001) 31561–31566. [PMID: 11397798]
2.  Tonon, T., Harvey, D., Larson, T.R. and Graham, I.A. Identification of a very long chain polyunsaturated fatty acid Δ4-desaturase from the microalga Pavlova lutheri. FEBS Lett. 553 (2003) 440–444. [PMID: 14572666]
3.  Meyer, A., Cirpus, P., Ott, C., Schlecker, R., Zähringer, U. and Heinz, E. Biosynthesis of docosahexaenoic acid in Euglena gracilis: biochemical and molecular evidence for the involvement of a Δ4-fatty acyl group desaturase. Biochemistry 42 (2003) 9779–9788. [PMID: 12911321]
4.  Zhou, X.R., Robert, S.S., Petrie, J.R., Frampton, D.M., Mansour, M.P., Blackburn, S.I., Nichols, P.D., Green, A.G. and Singh, S.P. Isolation and characterization of genes from the marine microalga Pavlova salina encoding three front-end desaturases involved in docosahexaenoic acid biosynthesis. Phytochemistry 68 (2007) 785–796. [PMID: 17291553]
5.  Zäuner, S., Jochum, W., Bigorowski, T. and Benning, C. A cytochrome b5-containing plastid-located fatty acid desaturase from Chlamydomonas reinhardtii. Eukaryot Cell 11 (2012) 856–863. [PMID: 22562471]
[EC 1.14.19.31 created 2015]