title: A 56,000 Mr phosphoseryl protein in PC12 cell lysates strongly associates with protein-A sepharose beads and was observed in immune complex kinase assays for PP60c-src.
abstract: Using an immune complex kinase assay to measure pp60c-src kinase activity, we have identified a 56,000 Mr protein (p56) from PC12 cell lysates that co-purified with pp60c-src by strong association with protein-A sepharose beads. The p56 protein was strongly phosphorylated on serine but no tyrosine or threonine phosphorylation was evident. However, pp60c-src was strongly phosphorylated on tyrosine, weakly phosphorylated on serine with no observed threonine phosphorylation. P56 was not a proteolytic breakdown product of pp60c-src, since it was neither tyrosine phosphorylated nor was it recognized by anti-src antibody. P56 was also not recognised by other antibodies to 56kD signalling molecules such as p56lck. The identify of p56 awaits further investigation but its appearance in immunoprecipitates of pp60c-src using protein-A sepharose beads is of interest but complicates the the interpretation of results from immune complex kinase assays in PC12 cells.
authors.affiliation: Section of Molecular Pharmacology, Wellcome Research Laboratories, Beckenham, Kent, England.
authors.forename: C
authors.initials: C
authors.lastname: Buensuceso
authors.forename: M V
authors.initials: MV
authors.lastname: Rogers
mesh_terms: D000818:Animals; D000936:Antigen-Antibody Complex / Q000276:immunology*; D002454:Cell Differentiation / Q000187:drug effects; D003429:Cross Reactions; D007163:Immunosorbent Techniques; D008863:Microspheres; D008970:Molecular Weight; D009363:Neoplasm Proteins / Q000302:isolation & purification / Q000378:metabolism; D015688:Oncogene Protein pp60(v-src) / Q000276:immunology; D016716:PC12 Cells / Q000737:chemistry* / Q000187:drug effects; D010750:Phosphoproteins / Q000302:isolation & purification / Q000378:metabolism*; D010766:Phosphorylation; D010768:Phosphoserine / Q000032:analysis; D011233:Precipitin Tests; D011499:Protein Processing, Post-Translational; D016392:Proto-Oncogene Proteins pp60(c-src) / Q000276:immunology* / Q000378:metabolism; D051381:Rats; D012685:Sepharose / Q000031:analogs & derivatives* / Q000378:metabolism; D013205:Staphylococcal Protein A
chemical_list: D000936:Antigen-Antibody Complex; D009363:Neoplasm Proteins; D015688:Oncogene Protein pp60(v-src); D010750:Phosphoproteins; D010768:Phosphoserine; D016392:Proto-Oncogene Proteins pp60(c-src); D012685:Sepharose; C042030:Staphylococcal protein A-sepharose; D013205:Staphylococcal Protein A