Demethylates proteins that have been reversibly carboxymethylated. Demethylates PPP2CB (in vitro) and PPP2CA. Binding to PPP2CA displaces the manganese ion and inactivates the enzyme (By similarity). [phosphatase 2A protein]-C-terminal L-leucine methyl ester + H2O = [phosphatase 2A protein]-C-terminal L-leucine + H(+) + methanol Binds PPP2CA and PPP2CB. Phosphorylated by SIK1 following increases in intracellular sodium, leading to dissociation from the protein phosphatase 2A (PP2A) complex and subsequent dephosphorylation of sodium/potassium-transporting ATPase ATP1A1. Belongs to the AB hydrolase superfamily.