Seasonal changes in the specific activities of the pentose phosphate pathway enzymes. G6PDH and 6PGDH and NADP-dependent isocitrate dehydrogenase in the bivalves Mytilus edulis, Ostrea edulis and Crassostrea gigas

Abstract

1.1. The levels of three cytoplasmic NADP-dependent dehydrogenases, glucose 6-phosphate (G6PDH), 6-phosphogluconate (6PGDH) and isocitrate dehydrogenase (ICDH) have been measured in the digestive gland and mantle tissues of Mytilus edulis, Ostrea edulis and Crassostrea gigas, at bimonthly intervals throught the year. The levels of malic enzyme in both tissues were found to be low.2.2. The results indicated that the pentose phosphate pathway enzymes, together with cytoplasmic NADP-linked isocitrate dehydrogenase are the major sources of NADPH in these tissues. The levels of G6PDH and 6PGDH were highest in the digestive gland of M. edulis and O. edulis, during the summer, whereas ICDH activity remained nearly constant throughout the year.3.3. The levels of G6PDH, 6PGDH and ICDH were determined in the eggs and larvae of M. edulis and in the larvae and spat of O. edulis and C. gigas. Relative to G6PDH and 6PGDH, there were higher levels of ICDH in the eggs and larvae, as compared with the adult tissues.