Mitochondrial citrulline synthesis in the ureagenic toadfish,Opsanus beta, is dependent on carbonic anhydrase activity and glutamine transport
✍ Scribed by Henry, Raymond P.; Walsh, Patrick J.
- Publisher
- John Wiley and Sons
- Year
- 1997
- Tongue
- English
- Weight
- 152 KB
- Volume
- 279
- Category
- Article
- ISSN
- 0022-104X
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✦ Synopsis
Mitochondria isolated from the liver of the Gulf toadfish Opsanus beta produce scitrulline in the presence of 5 mM glutamine. Citrulline production was inversely related to succinate concentration between 0 and 10 mM, with a maximal rate being achieved at 0.1 mM. When toadfish are induced to become ureagenic by crowding-associated stress, mitochondrial citrulline production increases by approximately 10-fold. Citrulline synthesis is dependent on intramitochondrial carbonic anhydrase (CA) activity, being inhibited by about 75% by both acetazolamide and methazolamide. The addition of exogenous CA did not increase mitochondrial citrulline production. Anesthetizing the fish with MS 222 prior to mitochondrial isolation resulted in the near elimination of the capacity for citrulline synthesis. Mitochondria were also shown to possess an inducible glutamine transport system. The Vmax for glutamine uptake increased threefold and the Km increased four-fold in ureagenic vs. ammoniogenic toadfish. The transport system is the second labile component of the overall ornithine-urea cycle to be identified, and it provides a link between the production of glutamine via cytoplasmic glutamine synthetase and its consumption via mitochondrial carbamoyl phosphate synthetase III.