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.
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 created 2015]