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 to the dehydrogenase TTHB247, ensuring that these toxic aldehydes are sequestered from cellular components. Is involved in the meta-cleavage pathway for the degradation of aromatic compounds. Appears to be stereospecific since it can cleave (4S)-4-hydroxy-2-oxopentanoate but not the (4R) isomer. Is not able to catalyze the aldol addition of 2-oxobutyrate with acetaldehyde; this indicates that the enzyme is specific for pyruvate as the carbonyl donor. (S)-4-hydroxy-2-oxopentanoate = acetaldehyde + pyruvate (S)-4-hydroxy-2-oxohexanoate = propanal + pyruvate Divalent metal cation. Has the highest activity with Co(2+) as cofactor, followed by Ni(2+) and Mn(2+). Mg(2+) and Ca(2+) are very poor metal cofactors. Appears to be allosterically activated by NADH. The catalytic efficiency is similar when using 4-hydroxy-2-oxopentanoate or 4-hydroxy-2-oxohexanoate as substrate. In the presence of NADH, exhibits a 2-fold increase in kcat. Has a half-life of 42 hours at 50 degrees Celsius. When TTHB246 is in complex with TTHB247, its half-life is reduced by approximately 30 hours. Homodimer. Can also form a heterotetramer composed of two aldolase (TTHB246) and two dehydrogenase (TTHB247) subunits. Upon complex formation, the aldolase shows a 5-fold increase in substrate affinity, while the dehydrogenase shows a 3-fold decrease; the kcat values of each enzyme are reduced by 2-fold when they are in a complex. Belongs to the 4-hydroxy-2-oxovalerate aldolase family.