Structures and stereochemistry of the very long alpha, omega-bifunctional alkyl species in the membrane of Sarcina ventriculi indicate that they are formed by tail-to-tail coupling of normal fatty acids.

Abstract

In a previous study, we demonstrated that Sarcina ventriculi is capable of adjusting to alterations in environmental conditions (such as increase in temperature, lowering of pH, or addition of exogenous organic solvents) by the synthesis of a family of alpha, omega-dicarboxylic acids ranging from 28 to 36 carbons long (Jung, S., et al. 1993. J. Biol. Chem. 268: 2828-2835). The chain lengths and relative abundance of the very long dicarboxylic acids found in S. ventriculi suggest that they may be formed after the perturbation by the (enzymatic) tail-to-tail combinations of existing regular monofunctional fatty acids and not completely de novo by direct 2-carbon addition of acetyl coenzyme A (CoA). If this were true, knowing the structures of the regular fatty acids, we can predict those of the very long chain bifunctional acids. In this work we present definitive chemical results that strongly support this mechanism. This was done by analyzing the structures and stereochemistry of the very long bifunctional species in the light of those of the regular monofunctional species. The exact structures of membrane fatty acid methyl ester derivatives components were determined by various spectroscopic and chemical methods including gas chromatographic (GC) analysis, gas chromatography-mass spectrometry (GC-MS), 1H and 13C nuclear magnetic resonance (NMR) spectroscopy, Fourier transform infrared (FTIR) spectroscopy, polarimetry, and reductive ozonolysis. This yielded precise structural and stereochemical information on the position of substitution of the acyl chain by methyl groups, position and configuration of double bonds, and optical activity. These results, coupled with the absence of intermediate length acyl species, indicated that the very long alkyl species (without exception) can be formed by tail-to-tail joining of existing fatty acids. The ideas of a dynamically regulated catalytic system is proposed.