Calmodulin-dependent phosphatase preferentially dephosphorylates a 28 kDa protein in human platelets.
1. Human platelets contain a calmodulin-dependent phosphatase (calcineurin) that has many properties similar to those of bovine brain calmodulin-dependent phosphatase. 2. The activity of calcineurin phosphatase accounts for a small fraction of the total phosphatase activity in human platelets. 3. Labeling of human platelets with 32P yielded many phosphoproteins. 4. Incubation of a lysate of the 32P-labeled platelets with bovine brain calmodulin-dependent phosphatase led to preferential dephosphorylation of a 28 kDa protein (P28), a minor component of platelet proteins. 5. P28 is one of several proteins that were rapidly labeled upon stimulation of platelets with thrombin. 6. Even though the enzyme is known to catalyze the dephosphorylation of many substrates in vitro, its apparent preference for P28 suggests that its activity is highly selective.
Pezzi
L
L
Department of Biochemistry, St Jude Children's Research Hospital, Memphis, TN 38101.
Merat
D L
DL
Winkler
M A
MA
Cheung
W Y
WY
D000818:Animals; D001792:Blood Platelets / Q000378:metabolism*; D001798:Blood Proteins / Q000378:metabolism*; D019703:Calcineurin; D002148:Calmodulin-Binding Proteins / Q000378:metabolism*; D002417:Cattle; D006801:Humans; D066298:In Vitro Techniques; D008970:Molecular Weight; D010749:Phosphoprotein Phosphatases / Q000378:metabolism*; D010750:Phosphoproteins / Q000097:blood*; D010761:Phosphorus Radioisotopes; D010766:Phosphorylation; D054648:Protein Phosphatase 2
D001798:Blood Proteins; D002148:Calmodulin-Binding Proteins; D010750:Phosphoproteins; D010761:Phosphorus Radioisotopes; D019703:Calcineurin; D010749:Phosphoprotein Phosphatases; D054648:Protein Phosphatase 2