Structural features of aluminium(III) complexes with bioligands in glutamate dehydrogenase reaction system--a review

Aluminium(III) complexes are essential for understanding the toxicity, bioavailability and transport mechanisms of aluminium in environmental and biological systems. Since elucidation of the exact structures of these weakly coordinated systems is very difficult, the structures of Al(III) complexes in glutamate dehydrogenase reactions system were investigated recently from the following four aspects: (1) Constitutional studies: The keto-enol tautomerism of the complexes between aluminium(III) ion and alpha-ketoglutarate ligands in acidic aqueous solutions was studied. It is clearly demonstrated that Al(III) can promote the keto-enol tautomerization of alpha-ketoglutarate. (2) Configurational studies: Compared with L-Glu, the complex stability of D-Glu-Al is stronger, especially for the tridentate species. The result was further supported by computational results in the molecular mechanics model with the UFF forcefield. It is implied that Al(III) complexation may favor the racemization from L- to D-amino acids. (3) Conformational studies: At biologically relevant pH and concentrations of Al(III) and NADH, Al(III) was found to increase the percentage of folded forms of NADH, which results in reducing the activity of the coenzyme NADH in the hollow-dehydrogenase reactions system. However, the conformations of NAD(+) and Al-NAD(+) are dependent upon the solvents and other ligands in the complexes. (4) Biological effects: The effects of Al(III) on the activity of the glutamate dehydrogenase-catalyzed reactions were studied by monitoring the differential-pulse polarography reduction current of NAD(+). At the physiologically relevant pH values (pH 6.5 and 7.5), the activity of the GDH enzyme was strongly dependent on the concentration of the Al(III) in the assayed mixture solutions.