Study on the stereoselectivity of inositol 1,4,5-trisphosphate recognition sites of bovine adrenal cortex.
Inositol 1,4,5-trisphosphate (InsP3) is an intracellular messenger generated from the hydrolysis of phosphatidylinositol 4,5-bisphosphate by phospholipase C in response to Ca(2+)-mobilizing stimuli. InsP3 interacts with a specific receptor responsible for the release of sequestered Ca2+ from an intracellular store. The purpose of the present study was to evaluate the relative affinities of the naturally occurring D-isomer of InsP3 and that of its L-stereoisomer for the InsP3 receptor and the InsP3 metabolizing enzymes from bovine adrenal cortex. The InsP3 receptor recognized D- and L-isomers with respective affinities of 4.8 nM and 7.3 microM. This high degree of selectivity was also reflected in the capacity of both isomers to mobilize Ca2+ from the microsomal preparation. The partially purified InsP3 kinase preparation was also able to discriminate between the two stereoisomers. The activity of the kinase was half-maximally inhibited in the presence of 11 microM L-InsP3, a value much higher than the Km of the kinase for D-InsP3 (0.4 microM). Both stereoisomers exhibited equipotent affinities (around 17 microM) for the particulate preparation of InsP3 phosphatase. The enzyme, however, appeared to hydrolyze L-InsP3 at a much slower rate. These results demonstrated that the different recognition sites for InsP3 were expressing distinct levels of stereoselectivity. This property, which is an important aspect of ligand-receptor interaction, could be exploited for the design of new selective drugs interfering with InsP3 action and metabolism.
Luong
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Department of Pharmacology, Faculty of Medicine, University of Sherbrooke, (Quebec), Canada.
Boulay
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Guillemette
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D000302:Adrenal Cortex / Q000378:metabolism*; D000818:Animals; D002118:Calcium / Q000378:metabolism; D015220:Calcium Channels; D002417:Cattle; D066298:In Vitro Techniques; D007293:Inosine Triphosphate / Q000378:metabolism*; D053496:Inositol 1,4,5-Trisphosphate Receptors; D008861:Microsomes / Q000378:metabolism; D010770:Phosphotransferases / Q000378:metabolism; D017853:Phosphotransferases (Alcohol Group Acceptor); D011755:Pyrophosphatases / Q000378:metabolism; D011956:Receptors, Cell Surface / Q000378:metabolism*; D018160:Receptors, Cytoplasmic and Nuclear; D013237:Stereoisomerism; D000097630:Inosine Triphosphatase
D002118:Calcium; D015220:Calcium Channels; D007293:Inosine Triphosphate; D053496:Inositol 1,4,5-Trisphosphate Receptors; D010770:Phosphotransferases; D017853:Phosphotransferases (Alcohol Group Acceptor); D011755:Pyrophosphatases; D011956:Receptors, Cell Surface; D018160:Receptors, Cytoplasmic and Nuclear; D000097630:Inosine Triphosphatase; C051038:Inositol 1,4,5-trisphosphate 3-kinase