HISTOCHEMISTRY OF OXIDASES IN SEVERAL TISSUES OF BIVALVE MOLLUSKS

Various tissues of the marine bivalve Mytilus galloprovincialis were a nalysed histochemically for oxidases capable of generating reactive ox ygen species (ROS) using the cerium-DAB technique. Incubations were pe rformed on unfixed cryostat sections using polyvinyl alcohol and semip ermeable membranes. High xanthine oxidoreductase and D-amino acid oxid ase (DAOX) activities were observed in kidney epithelial cells of muss els. DAOX also presented a strong activity in all the digestive epithe lia. No xanthine oxidase activity was observed in any of the mussel ti ssues tested suggesting the presence of an enzyme only showing dehydro genase activity. Mannitol oxidase, associated with special organelles called 'mannosomes' of terrestrial gastropods, presented a weak activi ty in the stomach epithelium and a strong specific activity in the hae mocytes. Only DAOX presented a discrete granular distribution compatib le with a peroxisomal compartmentalization. No urate oxidase activity could be demonstrated in tissues of mussels. These observations sugges t a role for peroxisomes in ROS generation and determine the tissues c apable of producing oxygen radicals in the digestive gland. This study raises the question of the behaviour of these enzymes in conditions i n which ROS-generating organic xenobiotics are accumulated in the dige stive gland of molluscs. (C) 1997 Academic Press Limited.