Purification and Characterisation of an Unusually Heat‐Stable and Acid/Base‐Stable Class I Fructose‐1,6‐bisphosphate Aldolase from Staphylococcus aureus

The fructose‐1,6‐biphosphate aldolase (EC 4.1.2.13) from Staphylococcus aureus ATCC 12600 was purified and biochemically investigated. It was found that this aldolase belongs to the class I type of aldolases since the fructose‐1,6‐bisphosphate cleavage activity was insensitive to high levels of EDTA. Like class I aldolases of higher organisms, the S. aureus aldolase activity is inhibited on incubation with the substrate dihydroxyacetone‐phosphate in the presence of NaBH₄. Furthermore, the aldolase activity is not stimulated by monovalent or divalent cations. This enzyme exhibits an extreme stability to high temperature, acid and base. The purified enzyme is not inactivated after heating at 97°C for 1.6 h. An incubation at 130°C for 10 min is necessary to destroy irreversibly the activity of the aldolase. The optimal temperature for activity, however, is 37°C. It is a monomer with a molecular weight of about 33000 and exhibits a relatively broad pH optimum ranging over pH 7.5–9.0. Apart from fructose 1,6–bisphosphate as substrate (K_m= 0.045 mM), this aldolase also revealed activity with fructose 1‐phosphate (K_m= 25 mM). The pH of the isoelectric point lies between 3.95 and 4.25.