Characterization of Brain Phosphoproteins

Abstract

1) About 15% of alkaline labile phosphorus was extracted from acetone-butanol dried powder of ox brain with 0.05M borate buffer, pH 9.0, and was fractionated by Sephadex G-100 gel filtration. There was a mutual transformation between the components which were excluded and retained by this gel filtration.
2) Two kinds of phosphoproteins (peaks I and II) were obtained from the buffer extracted residue by sonication, sodium dodecylsulfate treatment, ammonium sulfate fractionation, and Sephadex G-200 gel filtration. Both of them retained the capability to act as a substrate for protein kinase.
3) These phosphoproteins were purified 15.5 times in peak I, and 8 times in peak II, when calculated in terms of the ratio of phosphoprotein phosphorus to protein. Peak I was, although purified to a greater extent than peak II, still heterogeneous electrophoretically. Amino acid analysis revealed that both fractions contained only traces of proline and cysteine, much glutamic acid, aspartic acid, leucine, glycine, and alanine.