title: Phosphorylation-dephosphorylation states at different sites affect phosphoprotein phosphatase 1 activity.
abstract: We have previously reported that the binding of type I collagen to its receptor initiates platelet aggregation involving phosphoprotein phosphatase 1 (PP 1), which coprecipitates with the 65-kDa platelet type I collagen receptor. Phosphorylation of the anti-PP1 precipitation PP1 decreases its enzyme activity. In the present investigation, the mechanism of the decreased enzyme activity was studied by examining the phosphorylation of PP 1 on serine/threonine or tyrosine residues. Phosphoamino acid analysis of the PP 1 indicates that serine, threonine, and tyrosine can all be phosphorylated. We find that the activity of PP 1 decreases with serine/threonine phosphorylation but that phosphorylation of tyrosine residue activates enzyme activity. These results indicate that the activity of platelet phosphoprotein phosphatase 1 is controlled by phosphorylation and dephosphorylation states at multiple, different site(s).
authors.affiliation: Veterans Affairs Medical Center and the Department of Medicine and Biochemistry, University of Tennessee-Memphis, 38104, USA. TChiang@UTMEM2.UTMEM.edu
authors.forename: T M
authors.initials: TM
authors.lastname: Chiang
mesh_terms: D017868:Cyclic AMP-Dependent Protein Kinases / Q000494:pharmacology; D004789:Enzyme Activation / Q000187:drug effects; D006801:Humans; D010749:Phosphoprotein Phosphatases / Q000737:chemistry / Q000378:metabolism*; D010766:Phosphorylation; D010768:Phosphoserine / Q000032:analysis; D010769:Phosphothreonine / Q000032:analysis; D019000:Phosphotyrosine / Q000032:analysis; D054645:Protein Phosphatase 1; D019061:src-Family Kinases / Q000494:pharmacology
chemical_list: D010769:Phosphothreonine; D010768:Phosphoserine; D019000:Phosphotyrosine; D019061:src-Family Kinases; D017868:Cyclic AMP-Dependent Protein Kinases; D010749:Phosphoprotein Phosphatases; D054645:Protein Phosphatase 1