SEASONAL-VARIATION IN THE ANTIOXIDANT DEFENSE SYSTEMS OF GILL AND DIGESTIVE GLAND OF THE BLUE MUSSEL, MYTILUS-EDULIS

Seasonal variation in the level of glutathione (GSH) and in the activi ties of glutathione S-transferase (GST; EC 2.5.1.18), GSH-peroxidase ( EC 1.11.1.9) and catalase (EC 1.11.1.6) in both the gill and digestive gland of the blue mussel (Mytilus edulis) sampled from Cork harbour w ere evaluated. GSH peroxidase activities are generally lowest in the p eriod February-April. Catalase activity did not vary greatly over the year in the two tissues studied from two separate sampling sites. Leve ls are generally lower in the period December-April than in May-July. GSH levels fluctuated in both tissues with lowest levels occurring dur ing the winter period. GST activity increases in the period September- March in gill tissue but does not vary significantly in digestive glan d where levels are consistently lower. This enzyme may therefore carry out a tissue-specific role in protecting gill tissue against oxidativ e stress in winter.