Anaerobiospirillum succiniciproducens phosphoenolpyruvate (PEP) carboxykinase catalyses the reversible metal-dependent formation of oxaloacetate (OAA) and ATP from PEP, ADP and CO2. Mutations of PEP carboxykinase have been constructed where the residues His225 and Asp263, two residues of the enzyme's putative Mn2+ binding site, were altered. Kinetic studies of the His225Glu, and Asp263Glu PEP carboxykinases show 600- and 16 800-fold reductions in Vmax relative to the wild-type enzyme, respectively, with minor alterations in Km for Mn2+. Molecular modeling of wild-type and mutant enzymes suggests that the lower catalytic efficiency of the Asp263Glu enzyme could be explained by a movement of the lateral chain of Lys248, a critical catalytic residue, away from the reaction center. The effect on catalysis of introducing a negatively charged oxygen atom in place of Nε-2 at position 225 is discussed in terms of altered binding energy of the intermediate enolpyruvate.
- Anaerobiospirillum succiniciproducens
- Phosphoenolpyruvate carboxykinase
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