Regulates the mitochondrial permeability transition pore and is essential for cellular survival and development. H2O + O-phospho-L-seryl-[protein] = L-seryl-[protein] + phosphate H2O + O-phospho-L-threonyl-[protein] = L-threonyl-[protein] + phosphate Binds 1 Mg(2+) or Mn(2+) ion per subunit. Highly expressed in the heart, kidney, brain and liver and to a lesser extent in testis, lung, spleen and adipose tissue. Very low amount in muscle (at protein level). Also expressed in the thymus (at protein level) and the diaphragm. Significantly reduced in hypertrophied hearts. Belongs to the PP2C family.