title: Phosphodipeptide analysis of nonhistone nuclear proteins from Novikoff hepatoma ascites cells.
abstract: To study the sites of phosphorylation in nuclear proteins a simple method was developed for the isolation and  analysis of phosphodipeptides. Partial acid hydrolysates of unfractionated nonhistone nuclear proteins were subjected to Dowex-1 column chromatography followed by paper electrophoresis at pH 1.8. Phosphoserine- and phosphothreonine-containing dipeptides each had characteristic mobilities in the latter system. By subtractive Edman degradation these peptides were identified as having the general structure, X-PSer or X-PThr, where X is a nonphosphorylated amino acid. The two groups of phosphodipeptides were further purified into unique peptides by two-dimensional paper electrophoresis at pH 3.6 and 6.5. Amino acid analysis, and thus nearest neighbor analysis, of phosphodipeptides from nonhistone nuclear proteins revealed that a heterogeneous group of amino acids was on the amino terminal side of phosphoserine residues. In contrast, phosphothreonine residues were predominantly preceded by proline.
mesh_terms: D000596:Amino Acids / Q000032:analysis; D000818:Animals; D002467:Cell Nucleus / Q000032:analysis; D002868:Chromosomal Proteins, Non-Histone; D004151:Dipeptides / Q000032:analysis*; D006868:Hydrolysis; D008114:Liver Neoplasms, Experimental / Q000032:analysis*; D008297:Male; D010748:Phosphopeptides / Q000032:analysis*; D010766:Phosphorylation; D010768:Phosphoserine / Q000032:analysis; D010769:Phosphothreonine / Q000032:analysis; D051381:Rats
chemical_list: D000596:Amino Acids; D002868:Chromosomal Proteins, Non-Histone; D004151:Dipeptides; D010748:Phosphopeptides; D010769:Phosphothreonine; D010768:Phosphoserine