抄録
Nine phosphatase activities were separated from human platelets by DEAE-Sepharose CL-6B and AcA 44 column chromatography. Two of which were pNPP phosphatases and had little activity toward 32P-histone IIA. The other seven phosphatase fractions were inactive toward pNPP in the presence of EDTA, but could be activated by Mn++ or Mg++. Histone IIA phosphatase activities of these fractions were significantly increased by Mn++ or Mg++ (Fr D, F), even though a considerable amount of the activity was observed in the presence of EDTA. All of these protein phosphatase activities were inhibited by NaF, a protein phosphatase inhibitor. Among phosphoproteins in Triton X-100 lysate of thrombin stimulated platelets, 47k phosphoprotein was remarkably dephosphorylated in the presence of EDTA. Dephosphorylation of the other six phosphoproteins (250k, 180k, 120k, 95k, 47k, 28k) was enhanced and became apparent in the presence of Mn++ or Mg++, which was also inhibited by NaF. All histone IIA phosphatase fractions dephosphorylated eight cytoskeletal phosphoproteins (250k, 150k, 110k, 95k, 80k, 47k, 28k, 20k) without strict substrate specificities. Thus, it was suggested that protein phosphatases in platelets might play a role in the negative feed back mechanisms by dephosphorylating phosphoproteins involved in platelet reaction.
