A novel effect of vanadium ions: inhibition of succinyl-CoA synthetase

Effect of vanadate and vanadyl ions on the ATP-dependent succinyl-CoA synthetase (A-SCS) solubilized by Lubrol-PX from the rat brain mitochondria was tested. Vanadate added to the assay medium at 10(-5) mol.l-1 and 10(-4) mol.l-1 concentrations inhibited the enzyme activity by about 50% and 94%, respectively. When the enzyme was solubilized from the mitochondria preincubated with 10(-4) mol.l-1 and 10(-3) mol.l-1 vanadate, the residual inhibitions were 55% and 100% respectively. The vanadyl cation also induced inhibition of the A-SCS activity but the effect was less expressed. At 10(-4) mol.l-1 concentration only 20% inhibition was achieved. The A-SCS solubilized from the mitochondrial subfractions (perikaryal, light and heavy synaptosomal) differed neither in the activity of A-SCS nor in the susceptibility toward action of vanadium ions. A strong dependence of the vanadate inhibition on the concentration of succinate was observed. The above effect (50% inhibition) could be demonstrated only at saturating concentration of succinate (50 mmol.l-1). The mechanism of vanadium ions action as well as differences between vanadate and vanadyl ions effects are discussed.