EXPRESSION AND ACTIVITY OF CARBAMOYL-PHOSPHATE SYNTHETASE-III AND ORNITHINE UREA CYCLE ENZYMES IN VARIOUS TISSUES OF 4 FISH SPECIES

Previous studies have reported low activities of carbamoyl phosphate s ynthetase (CPSase) and other ornithine urea cycle enzymes in the liver of many teleost fishes, but it was not established if the CPSase was the urea cycle-related CPSase III or pyrimidine pathway-related CPSase II. The purpose of this study was to investigate the expression of th e urea cycle-related CPSase III and other ornithine urea cycle enzymes in the liver, muscle, intestine, and kidney of three adult teleost fi sh (common carp, Cyprinus carpio; goldfish, Carassius auratus; channel catfish, Ictalurus punctatus) and a holostean fish (bowfin, Amia calv a). In contrast to previous literature reports, CPSase III activity wa s absent from the liver of all fish studied. Surprisingly, CPSase III was present in the muscle of the common carp and bowfin and in the int estine of bowfin. Variable levels of the remaining urea cycle enzymes, as well as the pyrimidine nucleotide pathway related CPSase II were e xpressed by all tissues and fish examined. We conclude that hepatic CP Sase III expression may be relatively rare in teleost and holostean fi shes, but expression in extrahepatic tissues, particularly muscle, may be more typical. (C) 1998 Elsevier Science Inc.