Evidence of the activity of tyrosine kinase(s) and of the presence of phosphotyrosine proteins in pea plantlets

Homogenate fractions from etiolated pea plantlets showed tyrosine kinase activity when incubated with [32P]ATP and substrates like polyamino acid polymer (Glu-Ala-Tyr)n or [Val5]angiotensin II. When these tyrosine kinase substrates were recovered by high voltage electrophoresis, and analyzed by high pressure liquid chromatography after alkaline hydrolysis, yielded radioactive phosphotyrosine. The same product was obtained after acid hydrolysis of either endogenous or exogenous substrates. Phosphorylated polypeptides were extracted after sodium dodecyl sulfate gel electrophoresis of a pellet fraction incubated with [32P]ATP. After acid hydrolysis and high voltage electrophoresis, [32P]phosphotyrosine was found in gel bands with polypeptides of about 92 and 57 kDa. These results suggest that tyrosine kinase(s) and phosphotyrosine proteins are also present in higher plants.