Rotational relaxation of 1,6-diphenylhexatriene in membrane lipids of cells acclimated to high and low growth temperatures

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Abstract
Measurement of the time-resolved fluorescence depolarization of 1,6-diphenylhexatriene (DPH) in artificial bilayers of microsomal membrane lipids from Tetrahymena gave detailed information concerning the molecular motion of this probe and fluid properties of the membrane lipids which were obscured with steady-state methods. The rotational motion of DPH in these lipids from cells acclimated to 15.degree. and 39.5.degree. C growth temperatures was anisotropic, which agreed with recent time-resolved studies of this probe in synthetic phospholipid systems. Evaluation of DPH polarization data obtained from these lipid fractions at their respective growth temperatures showed differences in physical properties which suggested that viscosity per se, of the microsomal lipids was not as strictly regulated as in prokaryotic systems. Rotational relaxation of DPH in 39.5.degree. C microsomal lipids measured at its actual growth temperature, suggesting that the probe was partitioned into 2 dissimilar environments within the bilayer. Similar effects were observed in the microsomes of 39.5.degree. C cells by freeze-fracture EM following rapid cooling to 15.degree. C. Under these conditions, 2 distinct regions were observed on the fracture faces, suggesting a correlation between lipid phase phase changes and alterations in membrane structure.