Peroxisomes in digestive gland cells of the mussel Mytilus galloprovincialis Lmk. Biochemical, ultrastructural and immunocytochemical characterization.

The present study was undertaken because of the paucity of information on peroxisomes in molluscs and the increasing importance of these organisms as sensitive indicators of environmental pollution. Peroxisomes were identified by electron microscopy in all three main cell types of the digestive gland of the bivalve mollusc Mytilus galloprovincialis Lmk. They stained weakly with the alkaline diaminobenzidine reaction but showed distinct immunolabeling with an antibody against mammalian catalase by the postembedding protein A-gold procedure. In addition, mussel digestive gland peroxisomes were isolated by differential and metrizamide-density gradient centrifugation, and a 30-fold enrichment of catalase and a 20-fold enrichment of palmitoyl-CoA oxidase was obtained over the initial homogenate. By Western blotting, isolated peroxisomes crossreacted with antibodies to catalase and, furthermore, specific and prominent labeling of isolated peroxisomes was also demonstrated in thin sections incubated with anti-catalase antibodies. These observations establish that peroxisomes in molluscan digestive gland contain the peroxisomal marker enzymes catalase and acyl-CoA oxidase and that they can be labeled by cytochemical and immunocytochemical techniques. Further studies of alterations of molluscan peroxisomes by environmentally relevant xenobiotics are warranted.