WHY DO MITOCHONDRIA SYNTHESIZE FATTY-ACIDS - EVIDENCE FOR INVOLVEMENTIN LIPOIC ACID PRODUCTION

The function of acyl carrier protein (ACP) in mitochondria isolated fr om pea Leaves has been investigated, When pea Leaf mitochondria were l abeled with [2-C-14] malonic acid in vitro, radioactivity was incorpor ated into fatty acids, and, simultaneously, ACP was acylated, [1-C-14] Acetate was much less effective as a precursor for fatty acid synthesi s, suggesting that mitochondria do not possess acetyl-CoA carboxylase, The incorporation of radioactivity from [2-C-14] malonate into fatty acids and the labeling of ACP were inhibited by cerulenin and required ATP and Mg2+. These findings indicate that plant mitochondria contain not only ACP, but all enzymes required for de novo fatty acid synthes is, Over 30% of the radioactive products from pea mitochondria labeled with [2-C-14]malonate were recovered in H protein, which is a subunit of glycine decarboxylase and contains lipoic acid as an essential con stituent, In similar experiments, the H protein of Neurospora mitochon dria was also labeled by [2-C-14]malonate, The labeling of pea H prote in was inhibited by addition of cerulenin into the assay medium, Toget her, these findings indicate that ACP is involved in the de novo synth esis of fatty acids in plant mitochondria and that a major function of this pathway is production of lipoic acid precursors.