Urea cycle enzymes through the development of pacu (<Emphasis Type="Italic">Piaractus mesopotamicus</Emphasis>): the role of ornithine carbamoyl transferase |
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| Authors: | Paulo Sérgio Monzani Gilberto Moraes |
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| Institution: | (1) Laboratory of Adaptive Biochemistry, Department of Genetics and Evolution, Federal University of Sao Carlos, Rod Washington Luiz Km 235, CP 676, CEP 13565-905 Sao Carlos, SP, Brazil |
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| Abstract: | The present work reports the activities of urea cycle enzymes during the ontogenic development of the teleost pacu (Piaractus mesopotamicus). Urea cycle enzymes from the kidney and liver of adult fish were compared with those from the fish's embryonic phases. Samples
were evaluated over all phases of embryonic development, the larval period and alevin. Ammonia and urea concentrations were
determined during embryogenesis and in the plasma of adult fish. Except for carbamoyl phosphate synthetase-III (CPS-III),
all enzymes of the urea cycle were expressed in the larvae and alevins as well as in the liver and kidney of adult fish. In
spite of the low level of activity of the ornithine urea cycle (OUC) enzymes compared to those in mammals, and the low levels
of tissue urea concentration compared to ammonia, the ureogenesis was evaluated in pacu. Ammonia seems to be the main nitrogenous
waste during embryonic development. In this phase glutamine synthetase (GS) may play a role in ammonia detoxification, and
the OUC enzymes can be individually involved in functions other than urea production. The presence of ornithine carbamoyl
transferase (OCT) in all developmental phases of pacu and in the adult liver and kidney suggests that this enzyme is performing
different metabolic pathways. OCT in the kidney, wherein the activity is less than in the liver, should work in the biosynthesis
of polyamines and control the arginine plasma concentration given that renal arginase and argininosuccinate synthetase-argininosuccinate
lyase are more active than from the liver. We suppose that OCT during the embryogenesis is a control step regulating the cellular
concentration of ornithine for polyamines synthesis. |
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| Keywords: | Ornithine carbamoyl transferase Urea Ontogeny Ornithine-urea cycle Piaractus mesopotamicus Polyamines Putrescine |
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