Occurrence of lipid receptors inferred from brain and erythrocyte spectrins binding NaOH-extracted and protease-treated neuronal and erythrocyte membranes

It was previously shown in model systems that brain spectrin binds membrane phospholipids. In the present study, we analysed binding of isolated brain spectrin and red blood cell spectrin to red blood or neuronal membranes which had been treated as follows: (1). extracted with low ionic-strength solution, (2). the above membranes extracted with 0.1 M NaOH, and (3). membranes treated as above, followed by protease treatment and re-extraction with 0.1 M NaOH. It was found that isolated, NaOH-extracted, protease-treated neuronal and red blood cell membranes bind brain and red blood cell spectrin with moderate affinities similar to those obtained in model phospholipid membrane-spectrin interaction experiments. Moreover, this binding was competitively inhibited by liposomes prepared from membrane lipids. The presented results indicate the occurrence of receptor sites for spectrins that are extraction- and protease-resistant, therefore most probably of lipidic nature, in native membranes.