Calcineurin was shown previously to be inhibited by members of the tyrphostin family of tyrosine kinase inhibitors, with the most effective inhibition suggested to be caused by the presence of a conjugated side chain (Martin BL, Biochem Pharmacol 56: 483-488, 1998). Retinoids are a family of naturally occurring biomolecules having non-aromatic ring structures and conjugated side chains as substituents on the ring. Three oxidation states of the all-trans configuration of retinoids (retinol, retinal, and retinoic acid) were tested as effectors of calcineurin. Only retinoic acid was found to inhibit calcineurin effectively, with an IC50 value of approximately 50 μM. Retinol and retinal caused less than 30% inhibition at concentrations up to 100 μM. All three retinoids caused some precipitation of reaction components: retinoic acid and retinal above 50 μM, and retinol above 250 μM. Bacterial alkaline phosphatase was not inhibited by the retinoids, indicating that metal centers alone are insufficient for significant inhibition by retinoic acid. An aromatic ring was not required for inhibition and may not provide additional inhibition, in as much as an aromatic analog of retinoic acid (acitretin) showed less effective inhibition. These data are consistent with the presence of conjugated, unsaturated groups enhancing the inhibition of calcineurin. (C) 2000 Elsevier Science Inc.
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- Calmodulin-activated phosphatase