A soluble fatty acyl – acyl carrier protein synthetase from the bioluminescent bacterium Vibrio harveyi

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Abstract
An enzyme catalyzing the ligation of long chain fatty acids to bacterial acyl carrier protein (ACP) has been detected and partially characterized in cell extracts of the bioluminescent bacterium Vibrio harveyi. Acyl–ACP synthetase activity (optimal pH 7.5–8.0) required millimolar concentrations of ATP and Mg2+ and was slightly activated by Ca2+, but was inhibited at high ionic strength and by Triton X-100. ACP from either Escherichia coli (apparent Km = 20 μM) or V. harveyi was used as a substrate. Of the [14C]fatty acids tested as substrates (8–18 carbons), a preference for fatty acids ≤ 14 carbons in length was observed. Vibrio harveyi acyl–ACP synthetase appears to be a soluble hydrophilic enzyme on the basis of subcellular fractionation and Triton X-114 phase partition assay. The enzyme was not coinduced with luciferase activity or light emission in vivo during the late exponential growth phase in liquid culture. Acyl–ACP synthetase activity was also detected in extracts from the luminescent bacterium Vibrio fischeri, but not Photobacterium phosphoreum. The cytosolic nature and enzymatic properties of V. harveyi acyl–ACP synthetase indicate that it may have a different physiological role than the membrane-bound activity of E. coli, which has been implicated in phosphatidylethanolamine turnover. Acyl–ACP synthetase activity in V. harveyi could be involved in the intracellular activation and elongation of exogeneous fatty acids that occurs in this species or in the reactivation of free myristic acid generated by luciferase.Key words: acyl carrier protein, acyl – acyl carrier protein synthetase, fatty acid activation, bioluminescent bacteria.