PARTITION OF DDE IN SYNTHETIC AND NATIVE MEMBRANES DETERMINED BY ULTRAVIOLET DERIVATIVE SPECTROSCOPY

Partition coefficients of DDE (2,2-bis(p-chlorophenyl)-1,1-dichloroeth ylene) were determined, in model and native membranes, as a function o f temperature, lipid chain length, cholesterol content and DDE concent ration, by means of second derivative ultraviolet spectrophotometry. D DE incorporation increases with the temperature, since the partition v alues in dimyristoylphosphatidylcholine (DMPC), at 24, 30 and 37 degre es C, are 5722 +/- 138, 10356 +/- 763 and 14006 +/- 740, respectively. The insecticide incorporates better into bilayers of DMPC as compared with DPPC (dipalmitoylphosphatidylcholine). The partition decreases f rom 10355 +/- 763 in DMPC to 6432 +/- 613 in DPPC, at temperatures 5-7 degrees C above the midpoint of their transitions. The addition of ch olesterol to fluid membranes of DMPC depresses the partition of DDE. I n agreement with the results in models of synthetic lipids, the partit ion of DDE into native membranes increases with the temperature and de creases with the intrinsic cholesterol. It is concluded that a fluid m embrane favors the accumulation of DDE.