Plant Physiol. Journal of Pharmacology and Experimental Therapeutics
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Plant Physiology 94:214-220 (1990)
© 1990 American Society of Plant Biologists

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Metabolism and Enzymology

Involvement of Ferredoxin in Desaturation of Lipid-Bound Oleate in Chloroplasts 1

Hermann Schmidt and Ernst Heinz

Institut für Allgemeine Botanik der Universität Hamburg, Ohnhorststr. 18, 2000 Hamburg 52, Federal Republic of Germany

Intact spinach (Spinacia oleracea) chloroplasts, pulse-labeled with [14C]acetate, desaturate newly formed fatty acids as ester groups of monogalactosyl diacylglycerol in a subsequent chase in the dark. Rupture of pulse-labeled chloroplasts by addition of a detergent solution 3-([3-cholamidopropyl]dimethylammonio)-1-propane sulfonate preserves part of this desaturation activity. Direct addition of different free fatty acids together with appropriate cofactors to detergent-ruptured chloroplasts results in fatty acid labeling of monogalactosyl diacylglycerol. During subsequent incubation these lipid-linked fatty acids are desaturated, i.e. 18:1 to 18:2 and 18:3 and to a small extent also 16:0 to 16:3. The formation of 18:2 was also observed after incorporation of 18:1 into sulfolipid and phosphatidyl choline. Density gradient centrifugation separated a membrane fraction from detergent-ruptured chloroplasts which in the presence of appropriate cofactors incorporated 18:1 and 18:2 into the above-mentioned lipids. In the light, desaturation was dependent on added ferredoxin, whereas in the dark, in addition to ferredoxin NAD(P)H was also required. Preliminary evidence for the involvement of membrane-bound ferredoxin:NADP oxidoreductase (FNR) as a third component of desaturation in the dark was obtained by inhibitor studies including antibodies against FNR. Desaturation of lipid-bound 18:1 and 18:2 resembles stearoyl-ACP desaturation with respect to its requirement of reduced ferredoxin and oxygen.

1 This study was supported by grants from Bundesministerium für Forschung und Technologie and Fonds der Chemischen Industrie and represents part of a doctoral thesis to be submitted by H.S. to the Faculty of Biology at the University of Hamburg. Dedicated to Prof. Dr. W. Menke on the occasion of his eightieth birthday.




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