GULONOLACTONE OXIDASE ACTIVITY-DEPENDENT INTRAVESICULAR GLUTATHIONE OXIDATION IN RAT-LIVER MICROSOMES

The orientation of gulonolactone oxidase activity was investigated in rat liver microsomes, Ascorbate formation upon gulonolactone addition resulted in higher intravesicular than extravesicular ascorbate concen trations in native microsomal vesicles. The intraluminal ascorbate acc umulation could be prevented or the accumulated ascorbate could be rel eased by permeabilising the vesicles with the pore-forming alamethicin , The formation of the other product of the enzyme, hydrogen peroxide caused the preferential oxidation of intraluminal glutathione in gluta thione-loaded microsomes, In conclusion, these results suggest that th e orientation of the active site of gulonolactone oxidase is intralumi nal and/or the enzyme releases its products towards the lumen of the e ndoplasmic reticulum. (C) 1998 Federation of European Biochemical Soci eties.