Glycinebetaine stimulates,but NaCl inhibits,fatty acid biosynthesis in the moderately halophilic eubacterium HX

Total fatty acid synthetase (FAS) and cyclopropane fatty acid synthetase (CFAS) activities in cell-free lysates of the moderately-halophilic eubacterium HX, have been determined using radiolabelled malonyl-CoA and S-adenosylmethionine respectively as the precursor. The activities of FAS and CFAS were extremely low in vitro in 100 mM buffers, but were stimulated up to 100-fold by exogenous addition of the compatible-solute glycinebetaine to lysates; optimum activities of FAS and CFAS in vitro were obtained in 2–3 M concentrations of this compatible solute. In contrast, NaCl added to the lysate assay system was strongly inhibitory: CFAS was 97% inhibited by 1 M NaCl whereas FAS was less sensitive with 3 M NaCl giving 82% inhibition. When the culture medium salinity was raised from 1 to 3 M NaCl, the endogenous activity of CFAS measured in vitro in lysates without additional compatible solute was approximately doubled. This increase in CFAS activity is enough to account for the known increase in CFA content which occurs when culture medium salinity is raised, and the data are discussed in the context of the role of intracellular compatible solutes during haloadaptation of membrane lipid composition.Abbreviations FAS fatty acid synthetase - CFA cyclopropane fatty acid - CFAS cyctopropane fatty acid synthetase