Compartmentation of membrane phosphatidylethanolamine formed by base-exchange reaction in rat brain microsomes

The compartmentation of membrane phosphatidylethanolamine (PE) formed by base-exchange reaction in rat brain microsomal vesicles has been investigated. After labelling membrane PE by base-exchange in vitro, microsomal vesicles were treated with trinitrobenzenesulfonic acid (TNBS). The amount of membrane PE reacting with TNBS depends on the duration and the temperature of the reaction as well as on the TNBS concentration. It was found that almost all of the labelled PE molecules, but only about 24% of membrane PE, were accessible to TNBS, under very mild reaction conditions. It is concluded that PE labelled by base-exchange is completely localized in the cytoplasmic leaflet of microsomal vesicles.