Inhibition of porcine kidney betaine aldehyde dehydrogenase by hydrogen peroxide

Abstract

Renal hyperosmotic conditions may produce reactive oxygen species, which could have a deleterious effect on the enzymes involved in osmoregulation. Hydrogen peroxide was used to provoke oxidative stress in the environment of betaine aldehyde dehydrogenase in vitro. Enzyme activity was reduced as hydrogen peroxide concentration was increased. Over 50% of the enzyme activity was lost at 100 μM hydrogen peroxide at two temperatures tested. At pH 8.0, under physiological ionic strength conditions, peroxide inhibited the enzyme. Initial velocity assays of betaine aldehyde dehydrogenase in the presence of hydrogen peroxide (0–200 μM) showed noncompetitive inhibition with respect to NAD+ or to betaine aldehyde at saturating concentrations of the other substrate at pH 7.0 or 8.0. Inhibition data showed that apparent Vmax decreased 40% and 26% under betaine aldehyde and NAD+ saturating concentrations at pH 8.0, while at pH 7.0 Vmax decreased 40% and 29% at betaine aldehyde and NAD+ saturating concentrations. There was little change in apparent KmNAD at either pH, while KmBA increased at pH 7.0. Ki values at pH 8 and 7 were calculated. Our results suggest that porcine kidney betaine aldehyde dehydrogenase could be inhibited by hydrogen peroxide in vivo, thus compromising the synthesis of glycine betaine.