Manganese inactivation of renal betaine aldehyde dehydrogenase from swine

Abstract

Manganese is an essential micronutrient for mammals, however high manganese concentrations cause adverse health effects. Swine renal betaine aldehyde dehydrogenase catalyzes the synthesis of glycine betaine, which plays an important role in renal cells osmoregulation. In vitro inactivation of BADH was observed by incubating the purified enzyme in the presence of 1 mM MnCl2 under physiological and low ionic strength conditions. Enzyme inactivation followed first order kinetics in a monophasic process with an inactivation constant of 0.126 ± 0.011 min^-1 and 0.137 ± 0.017 at physiological and low ionic strength, respectively. Enzyme inactivation was not prevented by physiological ionic strength, nor by the substrates NAD+ and betaine aldehyde at saturated concentrations. The enzyme was reactivated with DTT and GSH. Native-PAGE of the inactivated enzyme showed no change in the tetrameric conformation. Intrinsic protein fluorescence studies demonstrated an increased exposure of the tryptophan residues to the aqueous solvent when the enzyme was incubated with Mn^2+. These results suggest that BADH inactivation by Mn^2+ may result from the oxidation of cysteines, which induces changes in the tertiary structure of the enzyme.