THE REAGGREGATION OF RAT-BRAIN MICROSOMAL-MEMBRANES AFTER THE TREATMENT WITH OCTYL-BETA-D-GLUCOPYRANOSIDE - A STUDY ON ETHANOLAMINE BASE-EXCHANGE

The ethanolamine base-exchange activity of rat brain microsomes has been studied after treating the membranes with the non-ionic detergent n-octyl-.beta.-D-glucopyranoside. The detergent could solubilize membrane lipid and protein. The concentrations of the detergent and of membrane protein were both important for this effect. The presence of disaggregating concentrations of octylglucopyranoside in the base-exchange incubation mixture strongly inhibited the incorporation of radioactive ethanolamine into lipid; however, the removal of the detergent through dialytic procedures before assaying the base-exchange reaction restored the enzymic activity almost completely. As shown by exposing the membranes to trinitrobenzenesulfonic acid (TNBS), the phosphatidylethanolamine (PE) which was newly synthesized by base-exchange was also compartmented in the microsomal membrane. The treatment with the detergent after the base-exchange reaction abolished the compartmentation of the newly synthesized lipid. However, if microsomes were solubilized and the detergent was removed by dialysis before the assay of base-exchange, the reassembly of membranes occurred with a recovery of the compartmentation of the newly synthesized PE. The presence of Ca2+ in the dialytic medium was important for the preservation of base-exchange activity, probably affecting the reassembly of membrane components.