title: Restriction of the in vitro and in vivo tyrosine protein kinase activities of pp60c-src relative to pp60v-src.
abstract: The tyrosine protein kinase activities of pp60c-src and pp60v-src were compared. The activities were qualitatively similar in vitro when the src proteins were bound in an immune complex with monoclonal antibody; both proteins utilized either ATP or GTP as phosphate donors, preferred Mn2+ to Mg2+, and had similar exogenous substrate specificities. The specific activity of pp60c-src was about 10-fold lower than that of pp60v-src for exogenous substrate phosphorylation but was only 1.1- to 2-fold lower than that of pp60v-src for autophosphorylation. Six glycolytic enzymes, including three not previously identified as substrates for pp60src phosphorylation, were phosphorylated by both pp60c-src and pp60v-src. Levels of pp60c-src fourfold higher than the amount of pp60v-src in src-plasmid-transformed cells did not detectably alter the level of phosphotyrosine in cellular proteins, but increasing the expression of pp60c-src another twofold (which induces cells to form foci in monolayer culture (P.J. Johnson, P.M. Coussens, A.V. Danko, and D. Shalloway, Mol. Cell. Biol. 5:1073-1083, 1985) resulted in a threefold increase in the level of cellular protein phosphotyrosine. Immunoprecipitation and analysis of the alkali-stable phosphoproteins by two-dimensional electrophoresis showed that, in contrast to pp60v-src-transformed cells, pp36 and enolase are only weakly phosphorylated in these high-level pp60c-src overexpresser cells. Even allowing for the in vitro differences in specific activities of phosphorylation, these results suggest that the pp60c-src tyrosine protein phosphorylating activity may be restricted relative to that of pp60v-src by additional in vivo mechanisms.
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D002460:Cell Line; D002645:Chickens; D006160:Guanosine Triphosphate / Q000378:metabolism; D007074:Immunoglobulin G / Q000378:metabolism; D066298:In Vitro Techniques; D007526:Isoelectric Point; D051379:Mice; D008970:Molecular Weight; D015688:Oncogene Protein pp60(v-src); D010766:Phosphorylation; D019000:Phosphotyrosine; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D016392:Proto-Oncogene Proteins pp60(c-src); D012191:Retroviridae Proteins / Q000378:metabolism*; D013379:Substrate Specificity; D014443:Tyrosine / Q000031:analogs & derivatives / Q000378:metabolism
chemical_list: D007074:Immunoglobulin G; D011518:Proto-Oncogene Proteins; D012191:Retroviridae Proteins; D019000:Phosphotyrosine; D014443:Tyrosine; D006160:Guanosine Triphosphate; D000255:Adenosine Triphosphate; D011505:Protein-Tyrosine Kinases; D015688:Oncogene Protein pp60(v-src); D016392:Proto-Oncogene Proteins pp60(c-src)