title: Reversal of Rous sarcoma-specific immunoglobulin phosphorylation on tyrosine (ADP as phosphate acceptor) catalyzed by the src gene kinase.
abstract: To determine the equilibrium constant of the reaction between ATP and protein-bound tyrosine we used as catalyst the highly purified Rous sarcoma src gene transcript. J. M. Sturtevant had earlier found (personal communication) that free tyrosine O-phosphate, upon hydrolysis with alkaline phosphatase in a calorimeter (37 degrees C, pH 9), yielded a delta H degrees of -2.8 kcal/mol (1 kcal = 4.18 kJ), less than half of that found in ATP hydrolysis. Experience with protein-bound serine phosphate (in phosvitin) had shown it to be energy rich [Rabinowitz, M. & Lipmann, F. (1960) J. Biol. Chem. 235, 1043-1050]. We wondered if the same is true for tyrosine phosphate when it is protein bound. From the equilibrium constant of 2.62 (at pH 6.5 and 5 mM Mg2+), we calculate a delta G degrees' of -9.48 kcal/mol for hydrolysis of protein-bound tyrosine phosphate, assuming an approximate delta G degrees' of -10 kcal/mol for hydrolysis of ATP. The experiments show that protein-bound tyrosine phosphate is energy rich, like serine phosphate in phosvitin.
mesh_terms: D000244:Adenosine Diphosphate / Q000378:metabolism; D000818:Animals; D001358:Avian Sarcoma Viruses / Q000201:enzymology; D007074:Immunoglobulin G / Q000378:metabolism; D007700:Kinetics; D015688:Oncogene Protein pp60(v-src); D019000:Phosphotyrosine; D011494:Protein Kinases / Q000378:metabolism*; D011817:Rabbits; D013816:Thermodynamics; D014443:Tyrosine / Q000031:analogs & derivatives* / Q000378:metabolism; D014764:Viral Proteins / Q000378:metabolism*
chemical_list: D007074:Immunoglobulin G; D014764:Viral Proteins; D019000:Phosphotyrosine; D014443:Tyrosine; D000244:Adenosine Diphosphate; D011494:Protein Kinases; D015688:Oncogene Protein pp60(v-src)