Inactivation of human glutamate dehydrogenase by aluminum

Abstract

Aluminum inactivated glutamate dehydrogenase (GDH) by a pseudo-first-order reaction at micromolar concentrations. A double-reciprocal plot gave a straight line with a k(inact) of 2.7 min(-1) and indicated the presence of a binding step prior to inactivation. The inactivation was strictly pH dependent and a marked increase in sensitivity to aluminum was observed as the pH decreased. At a pH higher than 8.5, no inactivation was observed. The completely inactivated GDH contained 2 mol of aluminum per mole of enzyme subunit monomer. When preincubated with enzyme, several chelators such as citrate, NaF, N-(2-hydroxyethyl) ethylenediaminetriacetic acid or ethylenediaminetriacetic acid efficiently protected the enzyme against the aluminum inactivation. In a related experiment, only citrate and NaF released the aluminum from the completely inactivated aluminum-enzyme complex and fully recovered the enzyme activity. Ferritin, NADP+, or nerve growth factor did not show any effects on the recovery of the aluminum-inactivated GDH activity. The dissociation constant for the aluminum-enzyme complex was calculated to be 5.3 microM. Although aluminum has been known to form a complex with nucleotides, no such effects were observed in the inactivation of GDH by aluminum as determined using GDHs mutated at the ADP-binding site, NAD+-binding site or GTP-binding site. Circular dichroism studies showed that the binding of aluminum to the enzyme induced a decrease in alpha helices and beta sheets and an increase in random coil. Therefore, inactivation of GDH by aluminum is suggested to be due to the conformational change induced by aluminum binding. These results suggest a possibility that aluminum-induced alterations in enzymes of the glutamate system may be one of the causes of aluminum-induced neurotoxicity.

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

“…In our electrochemical studies, 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 metal ion in the assayed mixture solutions. These experimental results are in good agreement with recently biological findings [2,5,6]. Therefore, it is concluded that the Al(III) bioavailability depends not only on the species and its structure, but also on its concentration and the pH value.…”

“…In the presence of a ring, like that of a double bond, prevents rotation, cis and trans isomers are possible. From the above constitutional studies on the keto-enol tautomerization of the Al(III) complexes with a-KG, it is also shown that different configurations of the isomers have [3][4][5]. The most stable enol-form isomers were isomers 4 and 5 based on the energy calculations.…”

“…It was also reported that Al(III) inactivated GDH by a pseudo-first-order reaction at micromolar concentrations. The inactivation of human GDH by Al(III) was due to the conformational change induced by Al(III) binding [5]. Accordingly, it can be concluded that the tricaboxylic acid (TCA) cycle has been reconfigured as a consequence of Al(III) stress [6].…”

Regulatory role of zinc during aluminium‐induced altered carbohydrate metabolism in rat brain

“…Al inhibits a large number of ATPdependent reactions and thus hampers energy-dependent processes (Silva et al, 2005;Szyperska et al, 2006). Reports have suggested that Al exposure can lead to impairment in glucose utilization, followed by altered activities of glucose-metabolizing enzymes, such as hexokinase and glutamate dehydrogenase (Yang et al, 2003;Dua et al, 2010). Zatta et al (2000) have observed alterations in the enzyme activities of both glycolytic and Kreb's cycle pathways.…”

Expression of a boiling-stable protein (BsCyp) in response to heat shock, drought and ABA treatments in Sorghum bicolor

“…We found that GDH activity was reduced in nodules at all the levels of Al stress. This unexpected decline in GDH may be because of its inactivation by Al, which induces a conformational change (induced by Al binding) similar to that observed in human GDH (Yang et al 2003) or a correlated inhibition resulting from a concomitant inhibition of nodule GS (Glevarec et al 2004). However, there was a significant increment in GDH activity in roots at the highest level of Al stress, although only one isoform could be detected.…”