alpha-chymotrypsin and phosphatidylinositol-4-phosphate

In human erythrocytes Ser/Thr- and Tyr-phosphorylations of cytoplasmic domain of band 3 are catalyzed by casein kinase I and Tyr-protein kinase respectively, both distributed between cytosol and membrane structures. The results reported here show that purified cytosolic Tyr-protein kinase activity, assayed on added substrates such as poly(Glu,Tyr)4:1 and isolated chymotryptic fragments of band 3 cytoplasmic domain (cdb3), is potently inhibited by PIP and even more by PIP2. Similar inhibitory effects are displayed by these polyphosphoinositides also on the endogenous Tyr-phosphorylation of band 3, when they are added to the isolated native membranes, thus suggesting their involvement in regulating in-vivo Tyr-phosphorylation of membrane proteins.

Topics: Adenosine Triphosphate; Anion Exchange Protein 1, Erythrocyte; Chymotrypsin; Erythrocytes; Humans; Hydrogen-Ion Concentration; Peptide Fragments; Phosphatidylinositol 4,5-Diphosphate; Phosphatidylinositol Phosphates; Phosphatidylinositols; Phosphoserine; Phosphotyrosine; Protein-Tyrosine Kinases; Tyrosine