The stability of glutathione peroxidase activity in plasma from cattle, pigs and sheep on storage in the presence and absence of glutathione.

Ovine, bovine and porcine plasma glutathione peroxidase (GSH-Px) activity decreased on storage at both 4 degrees C and 20 degrees C. The ovine and bovine enzymes were significantly less stable than the porcine enzyme. The addition of GSH to a final concentration of 2 mmol/L to plasma samples at the commencement of storage retarded the loss of both ovine and bovine plasma GSH-Px activity. The ovine enzyme was unique in that after inactivation by storage at 4 degrees C, incubation with GSH restored the enzyme activity. It is recommended that plasma GSH-Px should be assayed fresh, or otherwise stored at -20 degrees C.