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. Half maximal activity toward p-nitrophenylphosphate achieved with 3.7 mM of manganese ions. The gene represented in this entry is involved in disease pathogenesis. Belongs to the PP2C family. PubMed:18058037 has crystallized PPM1K in the presence of magnesium ions. However, PubMed:17336929 reported that no activity toward p-nitrophenylphosphate was seen in the absence of manganese ions and magnesium could not substitute for manganese.