Plant Physiol, October 2000, Vol. 124, pp. 681-692
Stearoyl-Acyl Carrier Protein and Unusual Acyl-Acyl
Carrier Protein Desaturase Activities Are Differentially
Influenced by Ferredoxin1
David J.
Schultz,
Mi Chung
Suh,2 and
John B.
Ohlrogge*
Department of Botany and Plant Pathology, Michigan State
University, East Lansing, Michigan 48824
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 
9 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 [14C]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 × hortorum) when compared with photosynthetic ferredoxin
isoforms. Heterotrophic ferredoxin also increases activity of the
ubiquitous 9 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.
1
This work was supported in part by the Michigan
Soybean Promotion Board and the U.S. Department of Agriculture,
National Research Initiative (grant no. 98-35505-6190) and by the
Michigan Agricultural Experiment Station.
2
Present address: Plant Cell Biotechnology Laboratory,
Korea Research Institute of Biosciences and Biotechnology, P.O. Box 115, Yusong Taejon, 305-600, Korea.
*
Corresponding author; e-mail ohlrogge{at}pilot.msu.edu; fax
517-353-1926.
© 2000 American Society of Plant Physiologists
