Activity of Acyl Carrier Protein Isoforms in Reactions of Plant Fatty Acid Metabolism

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Abstract
Two forms of spinach acyl carrier protein(ACP-I and ACP-II) have recently been characterized and found to be expressed in a tissue-specific manner (JB Ohlrogge, TM Kuo, 1985 J Biol Chem 260: 8032). To examine possible different functions for these ACP isoforms, we have tested purified preparations of spinach leaf ACP-I and ACP-II and Escherichia coli ACP in several in vitro reactions of fatty acid metabolism. Total de novo fatty acid synthesis and malonyl-CoA:ACP transacyclase do not appear to discriminate between acyl carrier protein isoforms. In contrast, the Km of oleoyl-ACP thioesterase for oleoyl-ACP-II is 10-fold higher than for oleoyl-CP-I, whereas the Km of acyl-ACP glycerol-3-phosphate acyl transferase is 5-fold higher for oleoyl-ACP-I than for oleoyl-ACP-II. A characterization of these reactions and a possible role for ACP isoforms in regulation of fatty acid metabolism in plants are described.