Stearoyl-acyl carrier protein and unusual acyl-acyl carrier protein desaturase activities are differentially influenced by ferredoxin.
Acyl-acyl carrier protein (ACP) desaturases function to position a single double bond into an acyl-ACP substrate and are best represented by the ubiquitous Delta9 18:0-ACP desaturase. Several variant acyl-ACP desaturases have also been identified from species that produce unusual monoenoic fatty acids. All known acyl-ACP desaturase enzymes use ferredoxin as the electron-donating cofactor, and in almost all previous studies the photosynthetic form of ferredoxin rather than the non-photosynthetic form has been used to assess activity. We have examined the influence of different forms of ferredoxin on acyl-ACP desaturases. Using combinations of in vitro acyl-ACP desaturase assays and [(14)C]malonyl-coenzyme A labeling studies, we have determined that heterotrophic ferredoxin isoforms support up to 20-fold higher unusual acyl-ACP desaturase activity in coriander (Coriandrum sativum), Thunbergia alata, and garden geranium (Pelargonium x hortorum) when compared with photosynthetic ferredoxin isoforms. Heterotrophic ferredoxin also increases activity of the ubiquitous Delta9 18:0-ACP desaturase 1.5- to 3.0-fold in both seed and leaf extracts. These results suggest that ferredoxin isoforms may specifically interact with acyl-ACP desaturases to achieve optimal enzyme activity and that heterotrophic isoforms of ferredoxin may be the in vivo electron donor for this reaction.
Schultz
D J
DJ
Department of Botany and Plant Pathology, Michigan State University, East Lansing, Michigan 48824, USA.
Suh
M C
MC
Ohlrogge
J B
JB
D000213:Acyl Carrier Protein / Q000378:metabolism*; D005288:Ferredoxins / Q000235:genetics / Q000378:metabolism* / Q000494:pharmacology; D006899:Mixed Function Oxygenases / Q000378:metabolism*; D010802:Phylogeny; D010944:Plants / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism / Q000494:pharmacology
D000213:Acyl Carrier Protein; D005288:Ferredoxins; D020033:Protein Isoforms; D006899:Mixed Function Oxygenases; C018747:acyl-(acyl-carrier-protein)desaturase