Inactivation of glucose-6-phosphate dehydrogenase by 4-hydroxy-2-nonenal: Selective modification of an active-site lysine

Incubation of glucose-6-phosphate dehydrogenase from Leuconostoc mesenteroides with 4-hydroxy-2-nonenal (HNE) results in a pseudo first-order loss of enzyme activity. The pH dependence of the inactivation rate exhibits an inflection around pH 10, and the enzyme is protected from inactivation by glucose 6-phosphate. Loss of enzyme activity corresponds with the formation of one carbonyl function per enzyme subunit and the appearance of a lysine-HNE adduct. The data presented in this paper are consistent with the view that the ε-amino group of a lysine residue in the glucose 6-phosphate-binding site reacts with the double bond (C₃) of HNE, resulting in the formation of a stable secondary amine derivative and loss of enzyme activity. We have described a mechanism by which HNE may, in part, mediate free radical damage. In addition, a method for the detection of the lysine-HNE adduct is introduced.