Phosphorylation of protein tyrosine by human erythrocyte casein kinase A

Abstract

Human erythrocyte casein kinase A, previously identified as a seryl, threonyl kinase, was found also to catalyze the phosphorylation of protein tyrosine. Phosphorylation of tyrosyl residues was detected in angiotensin-II and in several tyrosine containing synthetic peptides. In addition, phosphorylation on tyrosyl residues was also observed in alkylated bovine serum albumin and in band 3 and ankyrin purified from human erythrocyte membranes. The identification of phosphotyrosine was conducted using two-dimensional thin layer electrophoresis at pH 1.9 and 3.5 after acid hydrolysis of the phosphoproteins. It should be noted, however, that the major phosphorylation sites in band 3 and ankyrin catalyzed by casein kinase A were seryl and threonyl residues.