Calcineurin substrate is a peptide from the regulatory RII subunit of cAMP-dependent protein kinase. It can be used in the calcineurin activity assay. In Vitro: Calcineurin (PP2B), a serine/threonine phosphatase controlled by cellular calcium, has been implicated in a wide variety of biological responses including lymphocyte activation, neuronal and muscle development, neurite outgrowth, and morphogenesis of vertebrate heart valves^[1].