Some peroxisomal proliferators enhance membrane fluidity of liver peroxisomes.

The membrane fluidity of liver peroxisomes from normal and clofibrate-treated rats was investigated by using a fluorescence probe, 1-anilinonaphthalene-8-sulfonate (ANS). The excitation maximum of the probe was changed from 347 to 380 nm and the emission maximum from 493 to 463 nm in the presence of peroxisomes, and fluorescence intensity was enhanced more than 50 times. These results suggest that ANS was bound to the peroxisomal membrane. Fluorescence depolarization (P-value) was determined with such ANS-labeled peroxisomes. The P-values of peroxisomes from both normal and clofibrate-treated rats gradually decreased with increasing temperature, but that of clofibrate-treated peroxisomes was always smaller than that of normal peroxisomes. Pvalues were observed at 37°C for 60 min. The average P-value of normal peroxisomes was 0.270, while that of clofibrate-treated peroxisomes was 0.248. These results indicate that the membrane fluidity of liver peroxisomes in increased by the treatment with clofibrate. Treatment of rats with another inducer of liver peroxisome proliferation, di(2-ethylhexyl)phthalate, had an effect similar to that of clofibrate. However, alloxan-treated (diabetic) rats showed no change of peroxisomal membrane fluidity.