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Fluorescence of the conjugated polyene fatty acid, parinaric acid (PnA), was studied in membranes ofEscherichia coli during deenergization by colicin K. The free fatty acid and biosynthetically esterified forms ofcis -PnA (9,11,13,15-cis,trans,trans,cis -octadecatetraenoic acid), both of which are sensitive toE. coli lipid-phase transitions, were compared. When freecis -PnA was added exogenously to respiring bacteria, dissipation of the energized state of the membrane resulted in a dramatic increase incis -PnA fluorescence;all-trans -PnA was much less sensitive. Neither spectral shifts nor a change incis -PnA fluorescence polarization were observed. Analysis of the PnA content of extracellular fractions of deenergized and control cells revealed a difference in probe distribution: the membranes of energy-poisonedE. coli bound about 77% of exogenously addedcis -PnA, whereas membranes of actively respiring controls bound only about 44%. No fluorescence enhancement was observed in cells centrifuged to remove unboundcis -PnA before colicin treatment. Whencis -PnA was biosynthetically esterified to phospholipids of an unsaturated fatty acid auxotroph ofE. coli , the fluorescence did not change during membrane deenergization. In double-probe experiments, membrane deenergization resulted in fluorescence enhancement of exogenously addedN -phenyl-1-naphthylamine, without change in esterified PnA fluorescence. We conclude that deenergization ofE. coli membranes leads to increased binding and fluorescence of exogenously added PnA and cannot be detected from within the inner and outer membranes by PnA esterified in vivo.

journal of bacteriology

Membrane Deenergization by Colicin K Affects Fluorescence of Exogenously Added but Not Biosynthetically Esterified Parinaric Acid Probes in <i>Escherichia coli</i>

Membrane Deenergization by Colicin K Affects Fluorescence of Exogenously Added but Not Biosynthetically Esterified Parinaric Acid Probes in Escherichia coli