[Extraction and purification of tissue phosphopeptides].

We describe a method of extraction and partial purification of phosphopeptides isolated from pig brain or from the electrical organ of Torpedo marmorata. The extraction of the phosphopeptides was achieved by alcoholic 0,04 N potassium hydroxyde solution or by 10(-1) M KCL containing 10(-3) M EDTA and 10(-4) M DTT. After having tried various fractionation methods like ion exchange chromatography or gel filtration we chose chromatography on DEAE Sephadex followed by purification of the isolated fractions by Sephadex G 25 filtration. The most important phosphate fractions (one was purified to about 90 per cent) were characterized by the determination of the N/P ratio which was different from one phosphopeptide to another. The amino acid composition showed a high glycin, serine and "acid" amino acid content. The presence of phosphoserine was shown by electrophoresis and chromatography of a partial hydrolysate of in vivo 32P labelled phosphopeptides isolated from rat liver. The polyanionic structure of these phosphopeptides allow them to act as real ion exchangers which might be involved during active transport mechanisms in cellular membranes.