 Each subunit has a molecular weight of 36 kDa and contains an eight-stranded α/β barrel, which encloses lysine 229 (the Schiff-base forming amino acid that is key for catalysis).Though the majority of the overall structure of the aldolase enzyme is conserved amongst the three isozymes, four regions of the generic aldolase enzyme have been identified to be highly variable among isozymes.Such regions have been denoted isozyme-specific regions (ISR1-4).