Activities of UDPglucose Dehydrogenase, UDPglucuronyl Transferase, and Some Glycosidases of Freshwater Fish during the Adaptation to Salt Water

As reported by several workers1), the enzyme activity of glucuronide conjugation in fish is very weak or undetectable. However, SMITH2) noticed the fact that the marine fishes possess the apparent ability of glucuronide conjugation while the fresh water fishes do not, and he suggested that the mechanism may relate to the osmotic pressure of water surrounding fishes. In this experiment, using two species of Tilapia and rainbow trout, we investigated the levels of two enzymes which are responsible for the glucuronide conjugation, and three glycosidases of fish during the adaptation to salt water. Fishes showed a strong activity of UDPglucose dehydrogenase and a weak activity of UDPglucuronyl transferase. The “induction” was not found with the activities of both enzymes during the adaptation to salt water. The activities of UDPglucose dehydrogenase and β-glucosidase of liver, β-galactosidase and β-glucuronidase of kidney were decreased through the adaptation to salt water, while the activities of β-glucuronidase and β-galactosidase of liver, and β-glucosidase of kidney were increased.