Nitrogen metabolism of the South American lungfish Lepidosiren paradoxa

Carlisky, N.J.; Barrio, A

doi:10.1016/0305-0491(72)90099-5

Cited by 10 publications

(10 citation statements)

References 18 publications

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“…Although decreased ammonia production was suspected to occur during aestivation (Janssens and Cohen 1968;Carlisky and Barrio 1972), its importance has not been confirmed until recently Loong et al 2005;Ip et al 2005b). Since aestivating lungfishes undergo long-term fasting, problems associated with toxic ammonia being released from the degradation of excess amino acids as in fed animals no longer prevail, and there would be a low demand for ammonia detoxification.…”

Section: Cps Consists Of a Two-domain Gat Component And A Four-domainmentioning

confidence: 96%

Molecular characterization and mRNA expression of carbamoyl phosphate synthetase III in the liver of the African lungfish, Protopterus annectens, during aestivation or exposure to ammonia

et al. 2011

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This study aimed to obtain the full sequence of carbamoyl phosphate synthetase III (cps III) from, and to determine the mRNA expression of cps III in, the liver of P. annectens during aestivation in air, hypoxia or mud, or exposure to environmental ammonia (100 mmol l(-1) NH(4)Cl). The complete coding cDNA sequence of cps III from the liver of P. annectens consisted of 4530 bp, which coded for 1,510 amino acids with an estimated molecular mass of 166.1 kDa. The Cps III of P. annectens consisted of a mitochondrial targeting sequence of 44 amino acid residues, a GAT domain spanning from tyrosine 45 to isoleucine 414, and a methylglyoxal synthase-like domain spanning from valine 433 to arginine 1513. Two cysteine residues (cysteine 1337 and cysteine 1347) that are characteristic of N-acetylglutamate dependency were also present. The critical Cys-His-Glu catalytic triad (cysteine 301, histidine 385 and glutamate 387) together with methionine 302 and glutamine 305 affirmed that P. annectens expressed Cps III and not Cps I. A comparison of the translated amino acid sequence of Cps III from P. annectens with CPS sequences from other animals revealed that it shared the highest similarity with elasmobranch Cps III. A phylogenetic analysis indicates that P. annectens CPS III could have evolved from Cps III of elasmobranchs. Indeed, Cps III from P. annectens used mainly glutamine as the substrate, and its activity decreased significantly when glutamine and ammonia were included together in the assay system. There were significant increases (9- to 12-fold) in the mRNA expression of cps III in the liver of fish during the induction phase (days 3 and 6) of aestivation in air. Aestivation in hypoxia or in mud had a delayed effect on the increase in the mRNA expression of cps III, which extended beyond the induction phase of aestivation, reiterating the importance of differentiating effects that are intrinsic to aestivation from those intrinsic to hypoxia. Furthermore, results from this study confirmed that environmental ammonia exposure led to a significant increase in the mRNA expression of cps III in the liver of P. annectens, alluding to the important functional role of urea not only as a product of ammonia detoxification but also as a putative internal cue for aestivation.

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Section: Cps Consists Of a Two-domain Gat Component And A Four-domainmentioning

confidence: 96%

Molecular characterization and mRNA expression of carbamoyl phosphate synthetase III in the liver of the African lungfish, Protopterus annectens, during aestivation or exposure to ammonia

et al. 2011

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“…Of the three genera of extant lungfishes, the African Protopterus is most readily subject to environmental desiccation and regularly estivates in cocoons, the South American Lepidosiren also estivates but its burrows tend not to dry up completely, and the Australian Neocerutodus is fully aquatic (Carlinski & Barrio 1972, Funkhouser et al 1972. While estivating, Protopterus and Lepidosiren build up large quantities of urea in the tissues that circumvent ammonia toxicity and may contribute to adaptive metabolic repression (Smith 1930, Janssens 1964, Carlinsky & Barrio 1972.…”

Section: The Toadfishmentioning

confidence: 99%

“…While estivating, Protopterus and Lepidosiren build up large quantities of urea in the tissues that circumvent ammonia toxicity and may contribute to adaptive metabolic repression (Smith 1930, Janssens 1964, Carlinsky & Barrio 1972. Accordingly, the capacity for urea synthesis via the ornithine-urea cycle is highest in Proptopterus, essentially similar in Lepidosiren and quite low in Neoceratodus (Janssens & Cohen 1968, Goldstein et al 1967, Funkhouser et al 1972, Carlinski & Barrio 1972. Unlike other fishes, the African lungfish, Protopterus, possesses carbamoyl phosphate synthetase I and cytosolic arginase (Mommsen & Walsh 1989).…”

Section: The Toadfishmentioning

confidence: 99%

“…Unlike other fishes, the African lungfish, Protopterus, possesses carbamoyl phosphate synthetase I and cytosolic arginase (Mommsen & Walsh 1989). This is probably also true for Lepidosiren (Carlinski & Barrio 1972). It would be of interest to know whether the aquatic Australian lungfish, Neocerutodus, possesses CPS I like other lungfishes or CPS III like other aquatic fishes.…”

Section: The Toadfishmentioning

confidence: 99%

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Guppies, toadfish, lungfish, coelacanths and frogs: a scenario for the evolution of urea retention in fishes

Griffith

1991

Environ Biol Fish

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SynopsisThe question of how (and why) the ureosmotic strategy, characteristic of Latimeria chalumnae and the chondrichthians evolved is addressed. There are three requirements for ureosmotic regulation: urea synthesis via the ornithine-urea cycle, urea tolerance involving biochemical and physiological adjustments, and urea retention that requires renal, branchial, metabolic and reproductive adaptations. Several examples of lower vertebrates in which urea plays a physiological role are considered to see whether they might provide insight into the origin of ureosmotic regulation. The guppy shows high urea synthesis and retention during embryonic development, and it is possible that a developmental role of urea is a general phenomenon in fishes. The toadfish, thought to be an enigma with high urea synthesis in the absence of an obvious physiological role of urea, is ureotelic under some conditions. Its urea excretion is likely related to renal function and/or parental care. In lungfish high ureogenesis is associated with estivation in periodically dry habitats. The resultant hyperuremia prevents ammonia toxicity, inhibits water loss and may repress metabolism. Latimeria is a classic marine ureosmotic regulator in which urea is used as an osmolyte that allows osmotic equilibrium with sea water while maintaining low ion levels. Adults of the frog, Rana cancrivora, are also ureosmotic regulators in brackish water. A scenario is proposed that suggests how ureosmotic regulation could have evolved in Latimeria and other fishes. The ornithine-urea cycle (composed of an arginine synthetic pathway and a second pathway that splits arginine into urea) occurred in fossil anadromous agnathans. Here the first pathway functioned in the ammocoete-like larvae for the generation of arginine to supplement a protein-deficient diet of algae, whereas the arginase pathway was important in the embryo for vitellin catabolism. Gnathostome evolution was associated with trends towards large eggs and prolonged development, requiring a complete ornithine-urea cycle for ammonia detoxification in embryos. Retention of a complete ornithine-urea cycle throughout adult life (via paedomorphosis) would preadapt any relatively large, sluggish, euryhaline fish for ureosmotic regulation when it was exposed to sea water. It is suggested that ureosmotic regulators evolved from freshwater or anadromous ancestors that entered the marine habitat. Once early ureosmotic regulators were established in the sea there would have been strong selection for internal fertilization and development, as is seen in Latimeria and many elasmobranchs. It is suggested that ureosmotic regulation was a common strategy in Paleozoic marine gnathostomes.

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“…Many fish are capable of ureagenesis and there are several fish species for which a need for the urea cycle can be explained. Lungfish are periodically exposed to air and use the urea cycle to dispose of ammonia during periods of water shortage [5]–[8]. Sharks, skates and rays use urea as an osmolyte [9]–[14].…”

Section: Introductionmentioning

confidence: 99%

Expression Pattern and Biochemical Properties of Zebrafish N-Acetylglutamate Synthase

et al. 2014

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The urea cycle converts ammonia, a waste product of protein catabolism, into urea. Because fish dispose ammonia directly into water, the role of the urea cycle in fish remains unknown. Six enzymes, N-acetylglutamate synthase (NAGS), carbamylphosphate synthetase III, ornithine transcarbamylase, argininosuccinate synthase, argininosuccinate lyase and arginase 1, and two membrane transporters, ornithine transporter and aralar, comprise the urea cycle. The genes for all six enzymes and both transporters are present in the zebrafish genome. NAGS (EC 2.3.1.1) catalyzes the formation of N-acetylglutamate from glutamate and acetyl coenzyme A and in zebrafish is partially inhibited by L-arginine. NAGS and other urea cycle genes are highly expressed during the first four days of zebrafish development. Sequence alignment of NAGS proteins from six fish species revealed three regions of sequence conservation: the mitochondrial targeting signal (MTS) at the N-terminus, followed by the variable and conserved segments. Removal of the MTS yields mature zebrafish NAGS (zfNAGS-M) while removal of the variable segment from zfNAGS-M results in conserved NAGS (zfNAGS-C). Both zfNAGS-M and zfNAGS-C are tetramers in the absence of L-arginine; addition of L-arginine decreased partition coefficients of both proteins. The zfNAGS-C unfolds over a broader temperature range and has higher specific activity than zfNAGS-M. In the presence of L-arginine the apparent Vmax of zfNAGS-M and zfNAGS-C decreased, their Km app for acetyl coenzyme A increased while the Km app for glutamate remained unchanged. The expression pattern of NAGS and other urea cycle genes in developing zebrafish suggests that they may have a role in citrulline and/or arginine biosynthesis during the first day of development and in ammonia detoxification thereafter. Biophysical and biochemical properties of zebrafish NAGS suggest that the variable segment may stabilize a tetrameric state of zfNAGS-M and that under physiological conditions zebrafish NAGS catalyzes formation of N-acetylglutamate at the maximal rate.

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Nitrogen metabolism of the South American lungfish Lepidosiren paradoxa

Cited by 10 publications

References 18 publications

Molecular characterization and mRNA expression of carbamoyl phosphate synthetase III in the liver of the African lungfish, Protopterus annectens, during aestivation or exposure to ammonia

Molecular characterization and mRNA expression of carbamoyl phosphate synthetase III in the liver of the African lungfish, Protopterus annectens, during aestivation or exposure to ammonia

Guppies, toadfish, lungfish, coelacanths and frogs: a scenario for the evolution of urea retention in fishes

Expression Pattern and Biochemical Properties of Zebrafish N-Acetylglutamate Synthase

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