The G-protein-coupled receptor phosphatase: a protein phosphatase type 2A with a distinct subcellular distribution and substrate specificity.
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Phosphorylation of G-protein-coupled receptors plays an important role in regulating their function. In this study the G-protein-coupled receptor phosphatase (GRP) capable of dephosphorylating G-protein-coupled receptor kinase-phosphorylated receptors is described. The GRP activity of bovine brain is a latent oligomeric form of protein phosphatase type 2A (PP-2A) exclusively associated with the particulate fraction. GRP activity is observed only when assayed in the presence of protamine or when phosphatase-containing fractions are subjected to freeze/thaw treatment under reducing conditions. Consistent with its identification as a member of the PP-2A family, the GRP is potently inhibited by okadaic acid but not by I-2, the specific inhibitor of protein phosphatase type 1. Solubilization of the membrane-associated GRP followed by gel filtration in the absence of detergent yields a 150-kDa peak of latent receptor phosphatase activity. Western blot analysis of this phosphatase reveals a likely subunit composition of AB alpha C. PP-2A of this subunit composition has previously been characterized as a soluble enzyme, yet negligible soluble GRP activity was observed. The subcellular distribution and substrate specificity of the GRP suggests significant differences between it and previously characterized forms of PP-2A.
Receptor Protein-Tyrosine Kinases
Receptors, Cell Surface
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James B. Duke Distinguished Professor of Medicine
Dr. Lefkowitz’s memoir, A Funny Thing Happened on the Way to Stockholm, recounts his early career as a cardiologist and his transition to biochemistry, which led to his Nobel Prize win. Robert J. Lefkowitz, M.D. is James B. Duke Professor of Medicine and Professor of Biochemistry and Chemistry at the Duke University Medical Center. He has been an Investigator of the