PMID:3294837
| Citation |
Jackowski, S and Rock, CO (1987) Acetoacetyl-acyl carrier protein synthase, a potential regulator of fatty acid biosynthesis in bacteria. J. Biol. Chem. 262:7927-31 |
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| Abstract |
The first condensation reaction in the fatty acid biosynthetic pathway in Escherichia coli was rate-limiting as judged by analysis of the relative pool sizes of acyl carrier protein (ACP) thioester intermediates in vivo. Comparable concentrations of acetyl-ACP, malonyl-ACP, and nonesterified ACP were present during logarithmic growth, whereas long-chain acyl-ACP comprised a minor fraction of the total ACP pool. The antibiotic cerulenin was used to irreversibly inhibit both beta-ketoacyl-ACP synthases I and II. However, acyl-ACP formation in vivo was not blocked by this antibiotic, and short-chain (4-8-carbon) acyl-ACPs increased to 60% of the total ACP pool in cerulenin-treated cells. These data suggested that existence of a cerulenin-resistant condensing enzyme that was capable of catalyzing the initial steps in chain elongation. A unique enzymatic activity, acetoacetyl-ACP synthase, that specifically catalyzed the condensation of malonyl-ACP and acetyl-ACP was detected in E. coli cell extracts. Acetoacetyl-ACP synthase activity was not inhibited by cerulenin and was present in extracts prepared from a double mutant harboring genetic lesions in beta-ketoacyl-ACP synthases I and II (fabB20 fabF3). These data point to the condensation of malonyl-ACP and acetyl-ACP as the rate-controlling reaction in fatty acid biosynthesis and implicate acetoacetyl-ACP synthase as the pacemaker of fatty acid production in organisms and organelles that possess dissociated (Type II) fatty acid synthase systems. |
| Links | |
| Keywords |
Acyltransferases/isolation & purification; Acyltransferases/metabolism; Escherichia coli/enzymology; Escherichia coli/genetics; Fatty Acids/biosynthesis; Homeostasis; Kinetics; Mutation |
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