The uptake of Na-selenite in rat brain

Polyunsaturated fatty acids (PUFAs) occur in phospholipids of synapses of central nervous system (CNS). PUFAs may thus determine the fluidity of synaptosomal membranes and regulate neuronal transmission. It was therefore tempting to suggest an oxidative system in CNS protecting the membrane function, e.g., glutathione peroxidase (GSH-Px). In order to trace GSH-Px Wistar rats were loaded with 4800 kBq of⁷⁵Se sodium selenite. By means of gradient ultracentrifugation, particulate fractions of CNS were isolated and radioactivity as well as selenium dependent GSH-Px were estimated. The following data were obtained:

1. All fractions (myelin, synaptic vesicles, synaptosomes, mitochondria, and microsomes) contained⁷⁵Se.
2. After acetone precipitation of GSH-Px activity, fractionation on Sephadex G-150 revealed in all particulate fractions at least two peaks of radioactivity with GSH-Px activity.
3. The two GSH-Px peaks from the Sephadex filtration were freeze dried and applied on a hydrophobic T-gel column and eluted with decreasing molarity of ammonium sulfate from 1.5 to 0.05M. The first Sephadex peak with GSH-Px activity from myelin and the second peak with GSH-Px activity from synaptic vesicles could now be resolved into two different fractions of radioactivity on the T-gel. The remaining Sephadex G-150 peaks could only be resolved into one peak of radioactivity.
4. SDS-polyacrylamide gel electrophoresis of the T-gel peaks from all fractions showed a protein band with a mobility identical with that of human erythrocyte GSH-Px. The T-gel elution of myelin, synaptic vesicles and mitochondria gave rise to nearly pure CNS GSH-Px activity.

. The data presented support the idea that CNS fractions have membrane bound GSH-Px activity that may function as protecting enzymes towards oxidative stress in the brain.