Phosphorylation of the lysosomal enzyme binding receptor protein from monkey brain and evidence for a tyrosine kinase activity associated with it.

The lysosomal enzyme binding receptor protein prepared from monkey brain by phosphomannan-Sepharose affinity chromatography could undergo phosphorylation in the presence of [gamma-32P] ATP. The phosphorylated receptor protein appeared as a single radioactive band on polyacrylamide gel electrophoresis under nondenaturing conditions. Upon SDS-gel electrophoresis two radioactive bands, one corresponding to a high molecular weight (Mr greater than 116,000) component and another corresponding to Mr 45,000 were seen. Phosphoamino acid analysis showed that the receptor protein was phosphorylated on serine and tyrosine residues. The receptor protein could also phosphorylate histone on tyrosine residues exclusively. The phosphorylated receptor protein bound lysosomal enzymes to a lesser extent as compared to the non-phosphorylated receptor protein.