Studies on aluminum toxicity

Author

Sung-Woo Cho

Date of Award

12-1986

Degree Type

Thesis

Degree Name

Master of Science

Major

Biochemistry and Cellular and Molecular Biology

Major Professor

Jayant G. Joshi

Abstract

Long-term oral feeding of AlCl₃ to rats caused over a two-fold increase in the A1 content in the brain and reduced the activities of hexokinase and glucose-6-phosphate dehydrogenase by 24% (P<0.01). Dialysis reduced the A1 content to negligible levels and restored the activities of both enzymes. Nondialyzed homogenates were fractionated by gel filtration on Sephadex G-25 columns and the fractions assayed for A1. A1 in the dialysates eluted with the authentic AlCl₃. In vitro, G6P dehydrogenase (EC 1.1.1.49) from yeast was also inhibited -5 by A1 with a Ki of 1x10^-5 M. The inhibition was noncompetitive with respect to G6P and uncompetitive with respect to NADP⁺. Comparative study of the ability of G6P dehydrogenase to bind A1 was conducted by using an equilibrium gel filtration, Centrifree micropartition technique and ultraviolet difference spectroscopy. G6P dehydrogenase bound to A1 in a 1:1 molar ratio at A1 concentration ranging from 1x10^-3 to 1x10^-5 in the absence of substrate. None of the bound A1 was dialyzable at 4° both in 10 mM Tris/HCl, pH 7.4 and the same buffer containing 0.2 mM EDTA. The UV difference spectrum is characterized by an absorbance change at 229 nm. The origin of the UV difference spectrum may be understood as a partial modification of tyrosine residues. It seems that the protein undergoes a conformational change upon A1 binding. Kinetic data also showed a good agreement suggesting G6P dehydrogenase has one binding site for A1.

Thus it is suggested that in mammals at least one of the manifestations of long-term exposure to A1 is reduction in hexokinase activity which is the first enzyme in the utilization of glucose and in G6P dehydrogenase which regulates the concentration of NADP⁺ and NADPH.

Recommended Citation

Cho, Sung-Woo, "Studies on aluminum toxicity. " Master's Thesis, University of Tennessee, 1986.
https://trace.tennessee.edu/utk_gradthes/13668