Catalyzes the last step of the bacterial protocatechuate 4,5-cleavage pathway. Has a broad substrate specificity and catalyzes the aldol cleavage of 4-hydroxy-4-methyl-2-oxoglutarate, 4-hydroxy-2-oxoglutarate and 4-carboxy-4-hydroxy-2-oxoadipate, and the decarboxylation of oxaloacetate. Preferentially cleaves the L-isomer of 4-carboxy-4-hydroxy-2-oxoadipate, and has lower activity towards 4-hydroxy-4-methyl-2-oxoglutarate and 4-Hydroxy-2-oxoglutarate. Does not cleave 4-hydroxy-2-oxovalerate, citrate, 4-hydroxy-2-oxobutyrate, 2-oxoglutarate or fructose-1,6-bisphosphate. (4S)-4-hydroxy-2-oxoglutarate = glyoxylate + pyruvate (4R)-4-hydroxy-2-oxoglutarate = glyoxylate + pyruvate 4-hydroxy-4-methyl-2-oxoglutarate = 2 pyruvate 2-hydroxy-4-oxobutane-1,2,4-tricarboxylate = oxaloacetate + pyruvate H(+) + oxaloacetate = CO2 + pyruvate Divalent metal cations. Probably Mg(2+). Cleavage of 4-carboxy-4-hydroxy-2-oxoadipate, and to a lesser extent 4-hydroxy-4-methyl-2-oxoglutarate, is inhibited by lysine modification caused by diethyl pyrocarbonate. Decarboxylation of oxaloacetate is unaffected by diethyl pyrocarbonate. Inhibited by BeCl(2), CaCl(2), NiCl(2), BaCl(2), HgCl(2), SrSO(4), CrCl(3) and FeCl(3). Partially inhibited by p-chloromercuribenzoate and N-ethylmaleimide. Activated by inorganic phosphate, arsenate, phosphorous acid, acetyl phosphate, thiamine diphosphate, ADP, ATP and diphosphate. Optimum pH varies depending on the substrate used and phosphate concentration. In the absence of inorganic phosphate pH optima are 6.6 for L-4-carboxy-4-hydroxy-2-oxoadipate, 8.0 for D-4-carboxy-4-hydroxy-2-oxoadipate, 6.7 and 8.0 for DL-4-carboxy-4-hydroxy-2-oxoadipate, 8.3 for DL-4-hydroxy-4-methyl-2-oxoglutarate, 9.3 for DL-4-hydroxy-2-oxoglutarate and 8.8 for oxaloacetate. In the presence of 3 mM inorganic phosphate pH optima are more alkaline: 8.2 for L-4-carboxy-4-hydroxy-2-oxoadipate, 8.6 for D-4-carboxy-4-hydroxy-2-oxoadipate, 8.2 for DL-4-carboxy-4-hydroxy-2-oxoadipate, 8.9 for DL-4-hydroxy-4-methyl-2-oxoglutarate, 9.4 for DL-4-hydroxy-2-oxoglutarate and 8.9 for oxaloacetate. Stable at pH 6.0 to pH 9.5. Retains 50% of maximum activity after incubation at 54 degrees Celsius for 10 minutes. Homohexamer. By growth on aromatic carboxylates such as phthalate, terephthalate, m-hydroxybenzoate and p-hydroxybenzoate. Belongs to the LigK/PcmE family.