Catalyzes cleavage of the C(2)-C(3) bond in oxaloacetate and in (2R)-alkyl malate derivatives to form oxalate and acetate, and alkyl carboxylates and R-ketocarboxylates, respectively. H2O + oxaloacetate = acetate + H(+) + oxalate Binds 1 Mg(2+) ion per subunit. Can bind other divalent cations such as Mn(2+), Fe(2+) and Co(2+). Optimum pH is 7.0. Homodimer and homotetramer formed by a dimer of homodimer. Accumulates in senescing flower petals. By ethylene. Belongs to the isocitrate lyase/PEP mutase superfamily.