MeSH note : a 72 kDa protein-tyrosine kinase; ligation of the B cell antigen receptor leads to
the rapid phosphorylation of the enzyme on tyrosine & to the activation of the tyrosine
kinase activity of PTK72 for both substrate phosphorylation & autophosphorylation;
also undergoes a second phase of tyrosine phosphorylation & activation as B cells
progress through the late G(1) phase of the cell cycle;