Abstract
Carbamoyl phosphate is required for arginine and pyrimidine synthesis. In the arginine pathway, it is used in the ornithine transcarbamoylase (EC 2.1.2.1) reaction; in the pyrimidine pathway, it is used in the aspartate transcarbamoylase (EC 2.1.3.2) reaction. In Neurospora crassa, two pathway-specific enzymes catalyze the synthesis of carbamoyl phosphate, and two path-specific pools of carbamoyl phosphate are maintained. Histochemical studies show that ornithine transcarbamoylase is located in mitochondria, and, with less certainty, that aspartate transcarbamoylase is confined largely to nuclei. The enzymes that form carbamoyl phosphate are associated with the respective transcarbamoylases in the cell. Therefore, the segregation of carbamoyl phosphate pools could be accounted for by one or both organellar membranes, which demarcate two separate sites of carbamoyl phosphate metabolism in Neurospora. The alternative possibility that the enzyme complex that produces and consumes carbamoyl phosphate in the pyrimidine pathway could explain the channelling of carbamoyl phosphate, wholly or in part, is discussed.
Keywords: channelling, arginine, pyrimidines, electron microscope, eukaryotes
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Selected References
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- Bourget P. A., Natale P. J., Tremblay G. C. Pyrimidine biosynthesis in rat liver: studies on the source of carbamoylphosphate. Biochem Biophys Res Commun. 1971 Nov;45(4):1109–1114. doi: 10.1016/0006-291x(71)90452-9. [DOI] [PubMed] [Google Scholar]
- GRISOLIA S., COHEN P. P. The catalytic rôle of carbamyl glutamate in citrulline biosynthesis. J Biol Chem. 1952 Oct;198(2):561–571. [PubMed] [Google Scholar]
- Hoogenraad N. J., Levine R. L., Kretchmer N. Copurification of carbamoyl phosphate synthetase and aspartate transcarbamoylase from mouse spleen. Biochem Biophys Res Commun. 1971 Aug 20;44(4):981–988. doi: 10.1016/0006-291x(71)90808-4. [DOI] [PubMed] [Google Scholar]
- Issaly A. S., Cataldi S. A., Issaly I. M., Reissig J. L. Complementation on ribosomes between aspartate transcarbamylase mutants of Neurospora. Biochim Biophys Acta. 1970;209(2):501–511. doi: 10.1016/0005-2787(70)90747-1. [DOI] [PubMed] [Google Scholar]
- Jones M. E. Regulation of pyrimidine and arginine biosynthesis in mammals. Adv Enzyme Regul. 1970;9:19–49. doi: 10.1016/s0065-2571(71)80036-5. [DOI] [PubMed] [Google Scholar]
- Lue P. F., Kaplan J. G. Metabolic compartmentation at the molecular level: the function of a multienzyme aggregate in the pyrimidine pathway of yeast. Biochim Biophys Acta. 1970 Dec 16;220(3):365–372. doi: 10.1016/0005-2744(70)90268-8. [DOI] [PubMed] [Google Scholar]
- Lue P. F., Kaplan J. G. The aspartate transcarbamylase and carbamoyl phosphate synthetase of yeast: a multi-functional enzyme complex. Biochem Biophys Res Commun. 1969 Feb 21;34(4):426–433. doi: 10.1016/0006-291x(69)90399-4. [DOI] [PubMed] [Google Scholar]
- Merker H. J., Spors S. Electron microscopic demonstration of ornithine carbamoyltransferase in rat liver. Histochemie. 1969;17(1):83–88. doi: 10.1007/BF00306334. [DOI] [PubMed] [Google Scholar]
- Miller R. W. Dihydroorotate-quinone reductase of Neurospora crassa mitochondria. Arch Biochem Biophys. 1971 Sep;146(1):256–270. doi: 10.1016/s0003-9861(71)80063-2. [DOI] [PubMed] [Google Scholar]
- Mizutani A. Cytochemical demonstration of ornithine carbamoyltransferase activity in liver mitochondria of rat and mouse. J Histochem Cytochem. 1968 Mar;16(3):172–180. doi: 10.1177/16.3.172. [DOI] [PubMed] [Google Scholar]
- Moses H. L., Rosenthal A. S. Pitfalls in the use of lead ion for histochemical localization of nucleoside phosphatases. J Histochem Cytochem. 1968 Aug;16(8):530–539. doi: 10.1177/16.8.530. [DOI] [PubMed] [Google Scholar]
- Natale P. J., Tremblay G. C. On the availability of intramitochondrial carbamoylphosphate for the extramitochondrial biosynthesis of pyrimidines. Biochem Biophys Res Commun. 1969 Oct 22;37(3):512–517. doi: 10.1016/0006-291x(69)90945-0. [DOI] [PubMed] [Google Scholar]
- Spors S., Merker H. J. Fine structural localization of aspartate carbamoyltransferase in rat liver. Histochemie. 1969;17(1):78–82. doi: 10.1007/BF00306333. [DOI] [PubMed] [Google Scholar]
- Williams L. G., Bernhardt S. A., Davis R. H. Evidence for two discrete carbamyl phosphate pools in Neurospora. J Biol Chem. 1971 Feb 25;246(4):973–978. [PubMed] [Google Scholar]
- Williams L. G., Bernhardt S., Davis R. H. Copurification of pyrimidine-specific carbamyl phosphate synthetase and aspartate transcarbamylase of Neurospora crassa. Biochemistry. 1970 Oct 27;9(22):4329–4335. doi: 10.1021/bi00824a013. [DOI] [PubMed] [Google Scholar]
- Williams L. G., Davis R. H. Pyrimidine-specific carbamyl phosphate synthetase in Neurospora crassa. J Bacteriol. 1970 Aug;103(2):335–341. doi: 10.1128/jb.103.2.335-341.1970. [DOI] [PMC free article] [PubMed] [Google Scholar]