Reaction: (1) a γ-linolenoyl-[glycerolipid] + 2 ferrocytochrome b5 + O2 + 2 H+ = a (9Z,12Z)-octadeca-9,12-dien-6-ynoyl-[glycerolipid] + 2 ferricytochrome b5 + 2 H2O
(2) a stearidonoyl-[glycerolipid] + 2 ferrocytochrome b5 + O2 + 2 H+ = a (9Z,12Z,15Z)-octadeca-9,12,15-trien-6-ynoyl-[glycerolipid] + 2 ferricytochrome b5 + 2 H2O
Glossary: γ-linolenoate = (6Z,9Z,12Z)-octadeca-6,9,12-trienoate
stearidonate = (6Z,9Z,12Z,15Z)-octadeca-6,9,12,15-tetraenoate
dicranin = (9Z,12Z,15Z)-octadeca-9,12,15-trien-6-ynoic acid
Systematic name: Δ6 acyl-lipid,ferrocytochrome-b5:oxygen oxidoreductase (6,7-dehydrogenating)
Comments: The enzyme, characterized from the moss Ceratodon purpureus, converts the double bond at position 6 of γ-linolenate and stearidonate into a triple bond. The product of the latter, dicranin, is the main fatty acid found in C. purpureus. The enzyme contains a cytochrome b5 domain that acts as the direct electron donor to the desaturase active site. The enzyme also has the activity of EC 1.14.19.47, acyl-lipid (9-3)-desaturase.
Links to other databases: BRENDA, EXPASY, KEGG, MetaCyc, CAS registry number:
References:
1. Sperling, P., Lee, M., Girke, T., Zähringer, U., Stymne, S. and Heinz, E. A bifunctional Δ6-fatty acyl acetylenase/desaturase from the moss Ceratodon purpureus. A new member of the cytochrome b5 superfamily. Eur. J. Biochem. 267 (2000) 3801-3811. [PMID: 10848999]