Total oxyradical scavenging capacity in mussel Mytilus sp. as a new index of biological resistance to oxidative stress

The Total Oxyradical Scavenging Capacity (TOSC) has been characterized in various subcellular fractions from digestive gland of the mussel Mytilus sp.. A simple and sensitive gas-chromatographic assay is used for quantitating this new biochemical parameter. The method is based on the reaction between peroxyl radicals and α-keto-γ-methiolbutyric acid (KMBA) which is oxidized to ethylene: in the presence of cellular antioxidant competing with KMBA for peroxyl radicals, ethylene formation is quantitatively reduced. Whole cytosol from M. edulis exhibited slightly higher TOSC values than the Mediterranean species. Soluble antioxidants provided greater protection than proteins accounting for 70% of oxyradical scavenging capacity of whole cytosols. TOSC assay was suitable also for lipid-soluble antioxidants, and the analysis of the microsomal fraction confirmed the importance of membrane-associated antioxidants in protection against toxicity of reactive oxygen species (ROS). The analysis of TOSC in sentinel organisms is proposed as a new index of contaminant exposure, one which permits quantifiable assessment of the biological resistance to oxidative stress.