Description; Biochem/physiol Actions; Calcineurin is a cyclosporin-sensitive, calcium-regulated, serine-threonine protein phosphatase with broad substrate specificity. It is the major calmodulin-binding protein found in the brain. First identified as an inhibitor of the calmodulin activation of phosphodiesterase 3′:5′ cyclic nucleotide (PDE), calcineurin has similar effects on adenylate cyclase. Serves as a key enzyme involved in T-cell activation. Also involved in the hyperphosphorylation of tau protein in Alzheimer′s disease and has been shown to prevent calpain-mediated proteolysis of tau in differentiated PC12 cells.; Unit Definition; One unit will cause a 50% inhibition of the activated phosphodiesterase, 3′:5′-cyclic nucleotide (P 9529) activity when assayed with two units of activator (P 2277) and 0.1 mM Ca2+ in an enzyme coupled system at pH 7.5 at 30 °C.; Physical form; Lyophilized powder containing 0.5% EGTA, buffer salts and stabilizers.; Analysis Note; Sigma tests activity in 80 mM Tris, pH 7.5 with 65 mM KCl, 8 mM MgSO4 and 0.3% albumin.