Correlation between phosphorylation and kinase activity of a tyrosine protein kinase: p56lck

P56lck is the product of a cellular oncogene highly expressed in lymphoid cells. Tyrosine kinase activity was measured by using an exogenous substrate: polyamino acid glutamic acid-tyrosine (4:1) (PGT). Different levels of phosphorylation of p56lck were achieved by the utilisation of SH reagents and different lengths of incubation time. The phosphorylation of PGT was proportional to the level of phosphorylation of p56lck. Identical results were obtained with crude membrane preparations and with p56lck partially purified on immunecomplexes.