Reaction: (1) a (7Z,10Z)-hexadeca-7,10-dienoyl-[glycerolipid] + 2 reduced ferredoxin [iron-sulfur] cluster + O2 + 2 H+ = a (7Z,10Z,13Z)-hexadeca-7,10,13-trienoyl-[glycerolipid] + 2 oxidized ferredoxin [iron-sulfur] cluster + 2 H2O
(2) a linoleoyl-[glycerolipid] + 2 reduced ferredoxin [iron-sulfur] cluster + O2 + 2 H+ = an α-linolenoyl-[glycerolipid] + 2 oxidized ferredoxin [iron-sulfur] cluster + 2 H2O
Glossary: (9Z,12Z)-octadeca-9,12-dienoyl-[glycerolipid] = linoleoyl-[glycerolipid]
(9Z,12Z,15Z)-octadeca-9,12,15-trienoyl-[glycerolipid] = α-linolenoyl-[glycerolipid]
Other name(s): FAD7; FAD8
Systematic name: (7Z,10Z)-hexadeca-7,10-dienoyl-[glycerolipid],ferredoxin:oxygen oxidoreductase (13,14 cis-dehydrogenating)
Comments: This plastidial enzyme desaturates 16:2 fatty acids attached to the sn-2 position of glycerolipids to 16:3 fatty acids, and converts18:2 to 18:3 in both the sn-1 and sn-2 positions. It acts on all 16:2- or 18:2-containing chloroplast membrane lipids, including phosphatidylglycerol, monogalactosyldiacylglycerol, digalactosyldiaclyglycerol, and sulfoquinovosyldiacylglycerol. The enzyme introduces a cis double bond at a location 3 carbons away from the methyl end of the fatty acid. The distance from the carboxylic acid end of the molecule does not affect the location of the new double bond. cf. EC 1.14.19.25, acyl-lipid ω-3 desaturase (cytochrome b5) and EC 1.14.19.36, sn-1 acyl-lipid ω-3 desaturase (ferredoxin).
Links to other databases: BRENDA, EXPASY, KEGG, MetaCyc, CAS registry number:
References:
1. Iba, K., Gibson, S., Nishiuchi, T., Fuse, T., Nishimura, M., Arondel, V., Hugly, S. and Somerville, C. A gene encoding a chloroplast ω-3 fatty acid desaturase complements alterations in fatty acid desaturation and chloroplast copy number of the fad7 mutant of Arabidopsis thaliana. J. Biol. Chem. 268 (1993) 24099-24105. [PMID: 8226956]
2. McConn, M., Hugly, S., Browse, J. and Somerville, C. A mutation at the fad8 locus of Arabidopsis identifies a second chloroplast ω-3 desaturase. Plant Physiol. 106 (1994) 1609-1614. [PMID: 12232435]
3. Venegas-Caleron, M., Muro-Pastor, A.M., Garces, R. and Martinez-Force, E. Functional characterization of a plastidial ω-3 desaturase from sunflower (Helianthus annuus) in cyanobacteria. Plant Physiol. Biochem. 44 (2006) 517-525. [PMID: 17064923]