Exhibits oxaloacetate decarboxylase activity. Lacks any detectable aldolase activity with 4-hydroxy-2-oxopentanoate (HOPA), 4-hydroxy-2-oxohexanoate (HOHA) or other 4-hydroxy-2-oxoacids. H(+) + oxaloacetate = CO2 + pyruvate Activity is metal ion dependent and can be restored upon addition of excess Mn(2+). Activity is abolished upon incubation with Chelex and EDTA. kcat is 0.49 sec(-1). Homodimer. Belongs to the 4-hydroxy-2-oxovalerate aldolase family.