Evidence for autophosphorylation of hyaluronate binding protein and its enhanced phosphorylation in rat histiocytoma

This report documents for the first time the in vitro autophosphorylation of purified 68 kDa hyaluronate binding protein in presence of [32P] ATP. The rate of phosphorylation is proportional to the concentration of protein and to the time of incubation up to 5 min. By both phosphoamino acid and western blot analysis with antiphosphotyrosine antibodies, we have confirmed that the phosphorylation occurs at tyrosine residues. Immunoprecipitation with anti HA binding protein antibody shows a 5 fold increase in the phosphorylation in macrophage histiocytoma compared to normal macrophage. Supplementing hyaluronate with hyaluronate binding protein in the medium is further shown to enhance total protein phosphorylation in rat histiocytoma.