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  • Title: A new cGMP phosphodiesterase isolated from bovine platelets is substrate for cAMP- and cGMP-dependent protein kinases: evidence for a key role in the process of platelet activation.
    Author: Robichon A.
    Journal: J Cell Biochem; 1991 Oct; 47(2):147-57. PubMed ID: 1661738.
    Abstract:
    The biochemical differences among cGMP phosphodiesterases in platelets have not been thoroughly examined, primarily due to the lack of sufficient purified material. This report describes a simple method developed to isolate a specific bovine platelet cGMP phosphodiesterase. This enzyme is cytosolic in its native form and was purified to an apparent homogeneity by ion-exchange chromatography, affinity chromatography, and density gradient centrifugation. Cyclic GMP binds to a "pseudo-site" when the catalytic site is deprived of Mg++. The affinity for cGMP at alkaline pH in presence of EDTA and IBMX (Kd = 60 nM) suggests that the removal of Mg++ by EDTA converts the catalytic site to a binding site. A ligand affinity chromatography was designed to take advantage of these features. The core enzyme has a molecular weight 190,000 composed of 2 subunits (MW 95,000) and has a specific activity of 2.5 mumol/min/mg. Moreover, this enzyme was phosphorylated by cAMP- and cGMP-dependent protein kinases, suggesting that its activity could be indirectly regulated by cyclic nucleotides. Agents elevating cGMP and cAMP inhibit platelet activation by inhibiting protein kinase C and thrombin induced hydrolysis of phosphatidylinositol 4,5 diphosphate. The antiaggregating properties of some of these agents might therefore be attributed to the fact that they are inhibitors of phosphodiesterases.
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