Short-chain aliphatic alcohols increase rat-liver microsomal membrane fluidity and affect the activities of some microsomal membrane-bound enzymes.

n-Butyl and isoamyl alcohols decrease the steady-state fluorescence anisotropy of 1,6-diphenyl-1,3,5-hexatriene and enhance the efficiency of pyrene excimer formation when these probes are incorporated in rat-liver microsomal membrane, suggesting an increase in rotational and translational mobilities. Neither alcohol modifies NADH-ferricyanide reductase activity but both increase NADH-cytochrome c reductase activity. This was interpreted as an increase in the rate of lateral diffusion of the proteins cytochrome b5 and cytochrome b5 reductase as a consequence of the enhanced membrane lipid phase fluidity. Microsomal delta 9 and delta 6 desaturase activities in the presence of isoamyl alcohol were also studied. This alcohol decreases delta 9 desaturation when it is measured at a low substrate concentration (13 microM palmitic acid), but it is not modified when it is measured at a high substrate concentration (66 microM palmitic acid). delta 6 desaturation is diminished by isoamyl alcohol when it is measured with both 13 microM and 66 microM linoleic acid. The influence of isoamyl alcohol on the glucose-6-phosphatase system activity was also studied. In non-detergent-treated microsomes, isoamyl alcohol enhances glucose-6-phosphatase activity. However, if microsomes are previously treated with 0.1% Triton X-100 isoamyl alcohol does not modify this activity. The enhancement of the glucose 6-phosphate transport rate is not due to membrane permeability barrier disruption, since isoamyl alcohol does not modify mannose-6-phosphohydrolase latency. This would suggest that an increase in membrane lipid phase fluidity specifically activates glucose 6-phosphate transport across the membrane.