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BIOCHEMICAL PROCESSES AND MACROMOLECULAR STRUCTURES

Fatty Acid Biosynthesis in Mitochondria of Grasses: Malonyl-Coenzyme A Is Generated by a MitochondrialLocalized Acetyl-Coenzyme A Carboxylase¹

Botanik II, Universität Karlsruhe, 76128 Karlsruhe, Germany (M.F., E.G., S.S., H.-P.B.); Gesellschaft für Biotechnologische Forschung, 38124 Braunschweig, Germany (L.J.); Institut für Angewandte Genetik, Universität Hannover, D–30419 Hannover, Germany (H.-P.B.); and Molekulare Botanik, Universität Ulm, 89069 Ulm, Germany (S.B.)

We present biochemical evidence for the occurrence of a 250-kD multifunctional acetyl-coenzyme A carboxylase in barley (Hordeum vulgare) mitochondria. Organelles from 6-d-old barley seedlings were purified by differential centrifugation and Percoll density gradient centrifugation. Upon analysis by two-dimensional Blue-native (BN)/SDS-PAGE, an abundant 250-kD protein can be visualized, which runs at 500 kD on the native gel dimension. A similar 500-kD complex is present in etioplasts from barley. The mitochondrial 250-kD protein is biotinylated as indicated by specific reaction with an antibody directed against biotin. Peptide sequence analysis by electrospray ionization tandem mass spectrometry of the 250-kD proteins from both organellar fractions revealed amino acid sequences that are 100% identical to plastidic acetyl-coenzyme A carboxylase from wheat (Triticum aestivum). The 500-kD complex was also detected in wheat mitochondria, but is absent in mitochondrial fractions from Arabidopsis. Specific acetyl-coenzyme A carboxylation activity in barley mitochondria is higher than in etioplasts, suggesting an important role of mitochondria in fatty acid biosynthesis. Functional implications are discussed.

¹ This work was supported by the Deutsche Forschungsgemeinschaft and by the Fonds der Chemischen Industrie.

² These authors contributed equally to the work.

^* Corresponding author; e-mail braun{at}genetik.uni-hannover.de; fax 49511–7623608.

Received May 23, 2003; returned for revision June 23, 2003; accepted June 24, 2003.

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