Resolution of bovine brain calcineurin subunits: stimulatory effect of subunit B on subunit A phosphatase activity.

Calcineurin was dissociated into subunits A and B by SDS and the dissociated subunits were separated by Sephadex G-100 column chromatography in SDS. The phosphatase activity was associated with the A subunit and was detected only in the presence of MnCl2 of the various divalent cations tested. The Mn2+-dependent phosphatase of A subunit was stimulated (4-5-fold) by calmodulin. The subunit B increased only modestly Mn2+ stimulated phosphatase activity of subunit A but markedly increased it when assay also contained calmodulin. These results support the view that subunit B plays an important role in Mn2+/calmodulin regulation of subunit A phosphatase activity. They also lend further support to our earlier postulate ([1984] FEBS Lett. 169, 251-255) that Mn2+ is a powerful regulator of calcineurin phosphatase.