Low Mr GTP-binding proteins in human platelets: cyclic AMP-dependent protein kinase phosphorylates m22KG(I) in membrane but not c21KG in cytosol.
We have purified and characterized two kinds of GTP-binding proteins with Mr of 22,000 in human platelet membrane (main; m22KG(I), minor; m22KG(II)) (Nagata, K. and Nozawa, Y. (1988) FEBS Lett. 238, 90-94). In this study, the main GTP-binding protein (m22KG(I)) was found to be phosphorylated by cyclic AMP-dependent protein kinase (A-kinase), but not by protein kinase C. About 0.5 mol of phosphate was maximally incorporated into one mol of the protein and this phosphorylation was inhibited in the presence of A-kinase inhibitor. Phosphorylation of m22KG(I) did not alter either its GTP-binding or GTPase activity. When m22KG(I) was incubated alone or in the presence of 100 microM guanosine 5'-(3-O-thio)triphosphate (GTP gamma S) and then exposed to A-kinase, no significant changes in the level of phosphorylation were observed. On the other hand, the most abundant GTP-binding protein with Mr of 21,000 (c21KG) in human platelet cytosol, which was identified as a transformation suppressor gene product (rap 1 protein, smg p21 and Krev-1 protein), was not phosphorylated by A-kinase under the same condition. However, c21KG was phosphorylated by A-kinase after pretreatment with alkaline phosphatase.
Nagata
K
K
Department of Biochemistry, Gifu University School of Medicine, Japan.
Nagao
S
S
Nozawa
Y
Y
D000469:Alkaline Phosphatase / Q000494:pharmacology; D001792:Blood Platelets / Q000378:metabolism* / Q000648:ultrastructure; D002462:Cell Membrane / Q000378:metabolism*; D000242:Cyclic AMP / Q000494:pharmacology*; D003600:Cytosol / Q000378:metabolism*; D019204:GTP-Binding Proteins / Q000097:blood*; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D006160:Guanosine Triphosphate / Q000031:analogs & derivatives / Q000494:pharmacology; D006801:Humans; D007700:Kinetics; D008970:Molecular Weight; D010766:Phosphorylation; D047428:Protein Kinase Inhibitors; D011494:Protein Kinases / Q000378:metabolism*; D013873:Thionucleotides / Q000494:pharmacology
D047428:Protein Kinase Inhibitors; D013873:Thionucleotides; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D006160:Guanosine Triphosphate; D000242:Cyclic AMP; D011494:Protein Kinases; D000469:Alkaline Phosphatase; D019204:GTP-Binding Proteins