Electrochemical studies of aluminum and nano - form of aluminum compound dependent on coenzyme I - dehydrogenase activity
|School||Nanjing Normal University|
|Keywords||electrochemistry Al(Ⅲ) Al13 NAD~+/NADH-dependent dehydrogenase (GDH/MDH/ADH) conformation|
Aluminum has been recognized as a neurotoxic agent in animals and human beings for more than 100 years because it has shown interference with biological enzymatic activity in key metabolic pathways. It is also known that aluminum represents an important relevant etiological factor in several diseases, such as Alzheimer’ disease, Parkinson’s disease, rickets and anemia and so on. The increased recent studies in vitro have showed that Al(III) could inhibit the activity of enzyme which catalyzed the tricarboxylic acid cycle (TCA) and glycolytic cycle, thereby the production of energy generated by mitochondrial cell was badly affected. Therefore, it is reasonable to presume that aluminum with various speciations may display different effects on the activity of biological enzyme. In recent years, the potential effects of nanoparticles, which lead to unforeseen health or environmental hazards to human beings or other animal species, have raised considerable concerns. In this paper, we studied the effects of nanometer-sized tridecameric aluminum polycation (nano-Al13) and other Al species compound on the activity of several nicotinamide adenine dinucleotide (NAD+/NADH)-dependent dehydrogenase using electrochemical measurements in aqueous solutions. Moreover, fluorescence spectroscopy and circular dichroism (CD) spectrum was applied to study the proposed effect mechanism. The main results were listed as following:1.To study the effects of aluminum species on the activity of glutamate dehydrogenase (GDH), alcohol dehydrogenase (ADH) and malate dehydrogenase (MDH), a functionalized multi-wall nanotubes (MWNT) modified glass carbon electrode (GCE) was applied to monitor amperometric i-t curve for the oxidation of NADH. The experiment results showed that aluminum could inhibit the activity of GDH and ADH, but activate the MDH activity.2. The effect of aluminum on the enzyme activity varied with aluminum polynuclear species and pH values. Al(Ⅲ) showed the strongest effect at.pH 6.5, while the effect was decreased with the increasing of pH. The differences of the Al(Ⅲ) effect caused by pH may because that the species of Al(III) were diverse at different pH values and the speciation of Al(III) which more effectively interact with enzyme may become dominate at lower pH. The effect of Al13 was the highest at pH 7.5, and the effect level is similar at pH 6.5 and 8.5.The phenomenon could be explained by the reason that the stability of Al13 vary with pH. Al13 can stably exist at pH 7.5, whereas it may be depolymerized in acidic and alkaline solution.3. Fluorescence spectroscopy and circular dichroism (CD) spectrum was applied to study the possible effect mechanism of effect of Al(Ⅲ) and Al13 on the activity of NAD+/NADH-dependent dehydrogenase. The results showed that Al(III) and Al13 could induce the conformational changes of coenzyme NAD+ and NAD+/NADH-dependent dehydrogenase. When adding aluminum into the NAD+-hydrogenase system, aluminum occupied the active binding sites resulting in the occurrence of conformational changes in the NAD+ molecules, and then the unfavorable structural changes of recognition site for substrate and enzyme lead to the enzyme activity change. The binding of aluminum to the deydrogenase would induce transform betweenα-helices/β-sheets and random coil, which effected the induced-fit between enzyme and substrates and resulted in the change of enzyme activity.