Catalyzes the retro-aldol cleavage of both 4-hydroxy-2-oxopentanoate (HOPA) and 4-hydroxy-2-oxohexanoate (HOHA) to pyruvate and acetaldehyde or propanaldehyde, respectively. The aldehydes produced by this reaction are directly channeled from BphI to the dehydrogenase BphJ, ensuring that these toxic aldehydes are sequestered from cellular components. Is involved in the meta-cleavage pathway for the degradation of polychlorinated biphenyls (PCBs). Appears to be stereospecific since it can cleave (4S)-4-hydroxy-2-oxopentanoate but not the (4R) isomer. Also exhibits a secondary oxaloacetate decarboxylase activity. Finally, is also able to catalyze the reverse reaction, albeit much less efficiently, i.e. the condensation of aldehyde acceptors of two to three carbons in length with pyruvate. This aldol addition reaction is stereospecific; the condensation of acetaldehyde and pyruvate with BphI produces only the (4S)-4-hydroxy-2-oxopentanoate isomer. Aldehyde channeling in the BphI-BphJ complex can occur in reverse, from the dehydrogenase to the aldolase active sites, and the BphJ reductive deacylation reaction increases 4-fold when BphI is catalyzing the aldol addition reaction. Therefore, the BphI-BphJ enzyme complex exhibits unique bidirectionality in substrate channeling and allosteric activation. (S)-4-hydroxy-2-oxopentanoate = acetaldehyde + pyruvate (S)-4-hydroxy-2-oxohexanoate = propanal + pyruvate Divalent metal cation. Has the highest activity with Mn(2+) as cofactor. Can also use Cd(2+) at low concentrations (0.01-0.1 mM) or Co(2+), although with less efficiency. Mg(2+) and Ni(2+) are very poor metal cofactors. Competitively inhibited by oxalate. Also inhibited by high concentrations of Cd(2+) (1 mM) in vitro. Appears to be allosterically activated by aldehyde turnover occurring in BphJ, partly via NADH. The catalytic efficiency is similar when using 4-hydroxy-2-oxopentanoate or 4-hydroxy-2-oxohexanoate as substrate, but is 10-fold lower with 4-hydroxy-2-oxoheptanoate. It is also 25-fold higher when NADH is present than the value obtained without nucleotides. Moreover, the catalytic efficiency is similar when using acetaldehyde or propanaldehyde as substrate in the aldol addition reaction. Activity increases from pH 6.5 to 9. Xenobiotic degradation; polychlorinated biphenyl degradation. Heterotetramer composed of two BphI (aldolase) and two BphJ (dehydrogenase). The aldol addition reaction proceeds via a compulsory order mechanism, with pyruvate binding first. Belongs to the 4-hydroxy-2-oxovalerate aldolase family.