The possible involvement of a fatty acyl thioesterase in the termination of the synthesis of fatty acids in a psychrophilic bacterium, Vibrio sp. strain ABE-1

Abstract

In Vibrio sp. strain ABE-1, very long chain fatty acids with up to 30 carbon atoms were synthesized in vitro in the form of acyl-acyl carrier protein by a fatty acid synthetase that had been prepared from the cytosol fraction precipitated between 55 and 75% saturation with ammonium sulfate. In contrast, fatty acids with 10–18 carbon atoms, which are the usual acyl components in this bacterium, were synthesized in vitro when the unfractionated cytosol fraction was used as the source of catalytic activity. When partially purified fatty acid synthetase was used together with a subfraction that had been prepared from the cytosol fraction precipitated between 0 and 55% saturation with ammonium sulfate, 16-carbon fatty acids were recovered as the dominant free fatty acids, and fatty acids with more than 20 carbon atoms were not synthesized in vitro. Acyl-acyl carrier proteins and acyl-CoAs with 16-carbon fatty acids were preferentially hydrolyzed when this subfraction was used as the source of catalytic activity. These results suggest that (a) fatty acyl thioesterase(s) with high specificity for acyl-acyl carrier proteins with 16-carbon fatty acids regulate(s) acyl chain length. This activity could explain the high levels of 16-carbon fatty acids in this bacterium.Key words: acyl chain length regulation, fatty acyl thioesterase, acyl-ACP, fatty acid synthetase, psychrophilic bacteria, Vibrio sp.