Catalytic subunit of protein phosphatase 2A (PP2A), a serine/threonine phosphatase involved in the regulation of a wide variety of enzymes, signal transduction pathways, and cellular events. PP2A can modulate the activity of phosphorylase B kinase, casein kinase 2, mitogen-stimulated S6 kinase, and MAP-2 kinase. H2O + O-phospho-L-seryl-[protein] = L-seryl-[protein] + phosphate H2O + O-phospho-L-threonyl-[protein] = L-threonyl-[protein] + phosphate Binds 2 manganese ions per subunit. PP2A consists of a common heterodimeric core enzyme (composed of a 36 kDa catalytic subunit (subunit C) and a 65 kDa constant regulatory subunit (PR65) (subunit A)) that associates with a variety of regulatory subunits. Proteins that associate with the core dimer include three families of regulatory subunits B (the R2/B/PR55/B55, R3/B''/PR72/PR130/PR59 and R5/B'/B56 families), the 48 kDa variable regulatory subunit, viral proteins, and cell signaling molecules. Binds PPME1. May indirectly interact with SGO1, most probably through regulatory B56 subunits. Found in a complex with at least ARL2, PPP2CB, PPP2R1A, PPP2R2A, PPP2R5E and TBCD. Interacts with TBCD. Interacts with CTTNBP2NL. Interacts with PTPA. In prometaphase cells, but not in anaphase cells, localizes at centromeres. During mitosis, also found at spindle poles (By similarity). Reversibly methyl esterified on Leu-309 by leucine carboxyl methyltransferase 1 (Lcmt1) and protein phosphatase methylesterase 1 (Ppme1). Carboxyl methylation influences the affinity of the catalytic subunit for the different regulatory subunits, thereby modulating the PP2A holoenzyme's substrate specificity, enzyme activity and cellular localization (By similarity). Phosphorylation of either threonine (by autophosphorylation-activated protein kinase) or tyrosine results in inactivation of the phosphatase. Auto-dephosphorylation has been suggested as a mechanism for reactivation (By similarity). May be monoubiquitinated by NOSIP. Belongs to the PPP phosphatase family. PP-1 subfamily.