Changes in plasma membrane fluidity of corn (Zea mays L.) roots after Brij58 treatment

The detergent Brij 58 has been introduced to reverse plasma membrane (PM) v esicles from the right-side-out to the inside-out form. The aim of the pres ent work was to investigate the effect of Brij 58 on the formation of an AT P-dependent proton gradient and on the fluidity of the lipid phase of PM ve sicles. PMs of corn (Zen mays L.) roots were isolated by phase-partitioning . The fluidity of PMs was estimated by measurement of fluorescence polariza tion with 1-(4-trimelhylammoniumphenyl)-6-phenyl-1 hexatriene (TMA-DPH) and 1,6-diphenyl-1,3,5-hexatriene (DPH). The PMs of corn roots were relatively rigid. The hydrophobic part of the lipid bilayer was more fluid than the h ydrophilic part. After intercalation of Brij 58 into the lipid bilayer the membrane fluidity changed in a concentration-dependent manner. Treatment wi th the detergent Brij 58 increased the degree of fluorescence polarization for TMA-DPH, while it decreased it for DPH. This effect was saturated at a detergent-to-protein ratio of 1:4 for both fluorescence probes. Although th e biophysical characteristics of the membrane were changed after Brij 58 tr eatment, the formation of ATP-dependent proton gradients could still be mea sured with those vesicles. The generation of an ATP-dependent proton gradie nt with Brij 58-treated PM vesicles suggests that the detergent treatment i ndeed turned the originally right-side-out vesicles to sealed inside-out ve sicles. The limits of the effect caused by Brij 58 in the context of PM enz yme activities are discussed.