Seasonal variation of xanthine oxidoreductase activity in the digestive gland cells of the mussel Mytilus galloprovincialis: A biochemical, histochemical and immunochemical study

The activity and the tissue distribution of the oxygen radical producing en zyme xanthine oxidoreductase (XOR) were measured in the digestive gland of the common marine mussel Mytilus galloprovincialis Lmk along an annual cycl e. No xanthine oxidase (XOX) activity could be measured, the enzyme only di splaying xanthine dehydrogenase (XDH) activity in all the cases. This is in terpreted as a mechanism to avoid the harmful effects of the oxygen radical s that would be produced by XOX during periods following anoxic conditions at low tide. The highest XDH activities coincided with the late spring/earl y summer months, the activity maxima being recorded from May to July. Histo chemically XOR activity was very pronounced in duct and stomach epithelial cells as well as in the surrounding connective tissue and hemolymph vessels , the activity increasing towards the summer months. These seasonal variati ons in XDH or XOR activities are possibly linked to hormonal changes govern ing the reproductive cycle and to changes in food availability. The localiz ation of the protein in the connective tissue lining the hemolymph vessels was confirmed immunohistochemically using a polyclonal antibody against rat liver protein that cross-reacted specifically with a polypeptide of 150 kD a of molecular mass in homogenates of the digestive gland. This polypeptide was linked to cytosolic fractions isolated by differential centrifugation from mussel digestive glands. In paraffin sections the antibody labeled the digestive cells of digestive tubules, as well as the connective tissue sur rounding the hemolymph vessels, gonadal follicles, digestive epithelia and certain protozoan parasites. Taken together our results suggest that in the digestive gland of bi bivalve molluscs XOR is involved in the metabolism o f purines and in the scavenging of oxygen free radicals. (C) 1999 Editions scientifiques et medicales Elsevier SAS.