Title

Role of lipid saturation in modulating the effects of n-butanol on membrane phase behavior

Document Type

Conference Proceeding

Date of Original Version

12-1-2011

Abstract

Butanol has been identified by the US Department of Energy as an alternative fuel and a platform chemical for biorefining. When produced by fermentation, butanol concentrations are often low because of the low butanol tolerance of microorganisms. Low tolerance is attributed in part to butanol fluidization of cell membranes. One mechanism by which microbes adapt to butanol is by changing the ratio of saturated to unsaturated membrane lipids. To date, little is known regarding how the ratio of saturated to unsaturated lipids modulates the effects of butanol fluidization. In this research we examined the effects of n-butanol on the fluidity and phase behavior of synthetic lipid membranes composed of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) using fluorescence anisotropy and differential scanning calorimetry (DSC). For this system, temperatures below the melting temperature of DPPC (T m = 42 °C) yielded coexisting gel DPPC and fluid DOPC phases, while temperatures above T m yielded a fluid phase. DPPC alone exhibited membrane fluidization at butanol concentrations < 10 g/l and interdigitation at concentrations > 10 g/l butanol. These results, coupled with the large melting hysteresis that was observed between heating and cooling scans due to interdigitation, are consistent with previous studies. With increasing DOPC concentration (up to a 1:3 molar ratio of DPPC/DOPC) the fluidizing effects of n-butanol were enhanced in the coexisting gel DPPC phases. This effect may be attributed to greater partitioning of n-butanol via favorable packing within DOPC phases where the acyl tails are kinked due to the double bonds. The effects of DOPC concentration on DPPC interdigitation are less clear. T m hysteresis was reduced while the melting enthalpy hysteresis was increased with increasing DOPC concentration. This may reflect differences by which DOPC inhibits or enhances DPPC interdigitation with heating and cooling, or the partitioning behavior of n-butanol between DPPC and DOPC phases.

Publication Title

11AIChE - 2011 AIChE Annual Meeting, Conference Proceedings

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