J Exp Zool A Ecol Genet Physiol 2007 Mar 01;3073:163-75. doi: 10.1002/jez.a.364.

Sequence, expression and evolutionary relationships of carbamoyl phosphate synthetase I in the toad Xenopus laevis.

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The sequence of carbamoyl phosphate synthetase I (CPSase I) cDNA and expression of the enzyme in liver of the toad Xenopus laevis are reported. CPSase I mRNA increases 6-fold when toads are exposed to high salinity for extended periods of time. The deduced 1,494-amino acid sequence of the CPSase I is homologous to other CPSases and reveals a domain structure and conserved amino acids common to other CPSases. A serine residue (S287) is present where there is a cysteine residue required for glutamine-dependent activity in CPSase Types III and II (Type I CPSases utilize only ammonia as nitrogen-donating substrate). A sequence of DNA 964 bases upstream from the ATG start codon for the CPSase I gene is also reported. Phylogenetic analysis for 30 CPSase isoforms, including X. laevis CPSase I, across a wide spectrum of phyla is reported and discussed. The results are consistent with the views that eukaryotic CPSase II as a multifunctional complex evolved from prokaryotic CPSase II and that CPSase I in terrestrial vertebrates and CPSase III in fishes arose from eukaryotic CPSase II by independent events after the divergence of plants in eukaryotic evolution.

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???displayArticle.link??? J Exp Zool A Ecol Genet Physiol