| 1. |
- Lopez-Aparicio, Pilar, et al.
(författare)
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Insulin induced phosphorylation and activation of the cGMP-inhibited cAMP phosphodiesterase in human platelets
- 1992
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Ingår i: Biochemical and Biophysical Research Communications. - 1090-2104. ; 186:1, s. 517-523
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Tidskriftsartikel (refereegranskat)abstract
- Insulin induced phosphorylation and activation of the cGMP inhibited cAMP phosphodiesterase (cGI-PDE) in human platelets were demonstrated after isolation of the enzyme with specific polyclonal cGI-PDE antibodies. The demonstration of this insulin effect required suppression of basal cGI-PDE phosphorylation, through the use of the protein kinase inhibitor H-7 (1-(5-isoquinolinylsulfonyl)-2-methylpiperazine). The human platelet insulin receptor beta-subunit, previously identified as a 97 kDa polypeptide, was detected with the use of wheat germ agglutinin chromatography and anti-phosphotyrosine antibodies. These results suggest that insulin, through phosphorylation/activation of cGI-PDE, could decrease cAMP/cAMP dependent protein kinase (cAMP-PK) activity and thereby make the platelets more sensitive towards aggregating agents.
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| 2. |
- Rascon, Ana, et al.
(författare)
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Purification and properties of the cGMP-inhibited cAMP phosphodiesterase from bovine aortic smooth muscle
- 1992
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Ingår i: Biochimica et Biophysica Acta. - 0006-3002. ; 1134:2, s. 149-156
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Tidskriftsartikel (refereegranskat)abstract
- Pure cGMP-inhibited cAMP phosphodiesterase (cGI-PDE) in micrograms quantities was isolated from bovine aortic smooth muscle after more than 5000-fold purification using DEAE ion-exchange and affinity chromatography with a derivative of the specific cGI-PDE inhibitor cilostamide conjugated as a ligand to aminoethyl agarose (CIT-agarose). The cGI-PDE, which constituted about half of the high affinity cAMP-PDE activity of a tissue homogenate, was identified with a 105-kDa protein on SDS-PAGE through use of antibodies towards the human platelet, bovine cardiac and bovine adipose tissue cGI-PDE in Western blot and immunoprecipitation/immunoinactivation analysis. As observed during purification of the enzyme from other tissues the enzyme protein was exquisitely sensitive to proteolytic nicking during purification, resulting in several 30-77-kDa polypeptide fragments. Rapid immunoprecipitation from fresh tissue extracts was the only was found to partially prevent the proteolysis. The native enzyme had apparent molecular sizes of approx. 100,000 or, mainly approx. 220,000 by gel chromatography, presumably indicating the presence of monomeric and dimeric forms. The enzyme hydrolyzed cAMP and cGMP with normal Michaelis-Menten kinetics with Km of 0.16 and 0.09 microM, respectively, with Vmax for hydrolysis of cAMP of 0.3 compared to 3.1 mumol/min per mg protein for cAMP. The enzyme was potently and selectively inhibited by cGMP (IC50 approximately 0.25 microM) and the cardiotonic/vasodilatory drugs OPC-3911 (a cilostamide derivative), milrinone and CI-930 (IC50 approximately 0.05, 0.40 and 0.25 microM, respectively). The cGI-PDE was phosphorylated by cAMP-dependent protein kinase as has been reported for the analogous enzymes in heart, adipose tissue and platelets. The identification of a cGI-PDE in the aortic smooth muscle and its inhibitor specificity is consistent with the hypothesis that inhibition of this enzyme is important in the mechanism through which these drugs produce vasorelaxation.
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