Spin-labeling of Escherichia coli membrane by enzymatic synthesis of phosphatidylglycerol and divalent cation-induced interaction of phosphatidylglycerol with membrane proteins

Abstract

Escherichia coli membrane particulate fraction has been spin-labeled by incubating with sn- glycerol-3- phosphate , CTP, palmitoyl CoA and 12-nitroxide stearoyl CoA. Incorporation of the spin-labeled acyl chain into phosphatidylglycerol was confirmed. ESR spectrum of the spin-labeled phosphatidylglycerol in E. coli membrane consisted at least of two components; one due to the labels undergoing rapid anisotropic motions and the other due to strongly immobilized labels (the overall splitting value, approx. 58 G). The relative intensity of the two components was dependent on the concentration of divalent cations. The immobilized component decreased on treatment of the membrane with EDTA and increased on addition of Mg 2+ or Ca 2+. The spectrum at 1 mM Mg 2+ or Ca 2+ consisted almost only of the immobilized component. Spin-labeled phosphatidylglycerol in total lipid membrane showed ESR spectrum due to mobile labels and the spectrum was not affected appreciably by the divalent cations. The results suggest the divalent cation-mediated interaction of phosphatidylglycerol with proteins in E. coli membrane. Phosphoenolpyruvate-dependent uptake of methyl-α- d-glucoside was markedly accelerated by Mg 2+ · Ca 2+ was not effective for the enhancement. The divalent cation-induced interaction of phosphatidylglycerol with proteins was discussed in relation to the sugar transport.