Interactions of the neurotoxin 6-hydroxydopamine with glyceraldehyde-3-phosphate dehydrogenase

The neurotoxin 6-hydroxydopamine (6-OHDA) oxidised sulphydryl groups in glyceraldenyde-3-phosphate dehydrogenase (GAPDH) with loss of the dehydrogenase activity of the enzyme. 5-Hydroxydopamine behaved similarly at higher concentrations. This oxidation was accompanied by a transient rise in the acyl phosphatase (non-phosphorylating) activity of GAPDH. Treatment with arsenite resulted in loss of the acyl phosphatase activity and restoration of the dehydrogenase activity, consistent with the process involving sulphydryl-group oxidation to the corresponding sulphenate. Prolonged incubation with 6-OHDA resulted in a loss of both enzyme activities. Arsenite was unable to reverse this inhibition, indicating further oxidation, perhaps to sulphinate and sulphonate, to have occurred. RNA, but not DNA, was a partial inhibitor of both the dehydrogenase and acyl phosphatase activities of GAPDH, whereas DNA (both single- and double-stranded) was ineffective. Both single-stranded DNA and RNA inhibited the esterase activity of GAPDH, an activity that requires the absence of NAD+, in a process that was relieved at higher polynucleotide concentrations. Except at very high concentrations (1 mM), treatment of GAPDH 6-OHDA was ineffective at abolishing its to single-stranded DNA. Since GAPDH is an essential enzyme in glycolysis and also plays a role in apoptotic cell death, these results suggest that the effects on this enzyme may contribute to the neurotoxicity of 6-OHDA.