Inactivation of Bakers' yeast glucose 6-phosphate dehydrogenase by aluminum

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Abstract
Preincubation of yeast glucose-6-phosphate dehydrogenase (G6PD) with Al(III) produced an inactive enzyme containing 1 mol of Al(III)/mol of enzyme subunit. None of the enzyme-bound Al(III) was dissociated by dialysis against 10 mM Tris-HCl, pH 7.0, containing 0.2 mM EDTA at 4.degree.C for 24 h. Citrate, NADP+, EDTA, or Na protectd the enzyme against the Al(III) inactivation. The Al-(III)-inactivated enzyme, however, was completely reactivated only by citrate and NaF. The dissociation constant for the enzyme-aluminum complex was calculated to be 4 .times. 106M with NaF, a known reversible chelator for aluminum. Modification of histidine and lysine residues of the enzyme with diethyl pyrocarbonate and acetylsalicylic acid, respectively, inactivated the enzyme. However, the modified enzyme still bound 1 mol of Al(III)/mol of enzyme subunit. Circular dichroism studies showed that the binding of Al(III) to the enzyme induced a decrease in .alpha.-helix and .beta.-sheet and an increase in random coil. Therefore, it is suggested that inactivation of G6PD by Al(III) is due to the conformational change induced by Al(III) binding.

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