and are microaerophilic protozoa which rely on fermentative metabolism for energy generation. These organisms have developed a number of antioxidant defence strategies to cope with elevated O tensions which are inimical to survival. In this study, the ability of pyruvate, a central component of their energy metabolism, to act as a physiological antioxidant was investigated. The intracellular pools of 2-oxo acids in were determined by HPLC. With the aid of a dichlorodihydrofluorescein diacetate-based assay, intracellular reactive oxygen species generation by and suspensions was monitored on-line. Addition of physiologically relevant concentrations of pyruvate to and cell suspensions was shown to attenuate the rate of HO- and menadione-induced generation of reactive oxygen species. In addition, pyruvate was also shown to decrease the generation of low-level chemiluminescence arising from the oxygenation of anaerobic suspensions of . In contrast, addition of pyruvate to suspensions of respiring was shown to increase the generation of reactive oxygen species. These data suggest that (i) in and , pyruvate exerts antioxidant activity at physiological levels, and (ii) it is the absence of a respiratory chain in the diplomonads which facilitates the observed antioxidant activity.


Article metrics loading...

Loading full text...

Full text loading...



  1. Adam, R. D. (1991). The biology of Giardia spp. Microbiol Rev 55, 706-732. [Google Scholar]
  2. Biagini, G. A., Suller, M. T. E., Finlay, B. J. & Lloyd, D. (1997). Oxygen uptake and antioxidant responses of the free-living diplomonad Hexamita sp. J Eukaryot Microbiol 44, 447-453.[CrossRef] [Google Scholar]
  3. Biagini, G. A., McIntyre, P. S., Finlay, B. J. & Lloyd, D. (1998). Carbohydrate and aminoacid fermentation in the free-living primitive protozoon Hexamita sp. Appl Environ Microbiol 64, 203-207. [Google Scholar]
  4. Biagini, G. A., Kirk, K., Schofield, P. J. & Edwards, M. R. (2000). Role of K+ and amino acids in osmoregulation by the free-living microaerophilic protozoon Hexamita inflata. Microbiology 146, 427-433. [Google Scholar]
  5. Brand, K. A. & Hermfisse, U. (1997). Aerobic glycolysis by proliferating cells: a protective strategy against reactive oxygen species. FASEB J 11, 388-395. [Google Scholar]
  6. Brown, D. M., Upcroft, J. A. & Upcroft, P. (1993). Cysteine is the major low molecular weight thiol in Giardia duodenalis. Mol Biochem Parasitol 61, 155-158.[CrossRef] [Google Scholar]
  7. Brown, D. M., Upcroft, J. A. & Upcroft, P. (1995). Free-radical detoxification in Giardia duodenalis. Mol Biochem Parasitol 72, 47-56.[CrossRef] [Google Scholar]
  8. Brown, D. M., Upcroft, J. A. & Upcroft, P. (1996). A thioredoxin reductase-class of disulphide reductase in the protozoan parasite Giardia duodenalis. Mol Biochem Parasitol 83, 211-220.[CrossRef] [Google Scholar]
  9. Brown, D. M., Upcroft, J. A., Edwards, M. R. & Upcroft, P. (1998). Anaerobic bacterial metabolism in the ancient eukaryote Giardia duodenalis.Int J Parasitol 28, 149-164.[CrossRef] [Google Scholar]
  10. Brugerolle, G. (1974). Contribution a l’etude cytologique et phyletique des diplozaires (zoomastigophorea, diplozoa, Dangeard 1910). Protistologica 1, 83-90. [Google Scholar]
  11. Buchmann, K., Uldal, A. & Lyholt, H. C. K. (1995). Parasite infections in Danish trout farms. Acta Vet Scand 36, 283-298. [Google Scholar]
  12. Dando, P. R., Fenchel, T., Jensen, P., O’Hara, S. C. M., Niven, S. J. & Schuster, U. (1993). Ecology of gassy, organic-rich sediment in a shallow subtidal area on the kattegat coast of Denmark. Mar Ecol Prog Ser 100, 265-271.[CrossRef] [Google Scholar]
  13. Dimopoulos, M., Bagnara, A. S. & Edwards, M. R. (2000). Characterisation and sequence analysis of a carbamate kinase gene from the diplomonad Hexamita inflata. J Eukaryot Microbiol 47, 499-503.[CrossRef] [Google Scholar]
  14. Edwards, M. R., Payne, K. D., Wilson, J. R. & Schofield, P. J. (1994). Giardial aminotransferases. In Giardia from Molecules to Disease , pp. 189-191. Edited by R. C. A. Thompson, J. A. Reynoldson & A. J. Lymbery. Wallingford:CAB International.
  15. Fenchel, T., Bernard, C., Esteban, G., Finlay, B. J., Hansen, P. J. & Iversen, N. (1995). Microbial diversity and activity in a Danish fjord with anoxic deep water. Ophelia 43, 45-100.[CrossRef] [Google Scholar]
  16. Halliwell, B. & Gutteridge, J. M. C. (1999).Free Radicals in Biology and Medicine. Oxford: Oxford University Press.
  17. Hayashi, T., Tsuchiya, H., Todoriki, H. & Naruse, H. (1982). High-performance liquid chromatography determination of alpha-keto acids in human urine and plasma. Anal Biochem 122, 173-179.[CrossRef] [Google Scholar]
  18. Holleman, A. F. (1904).Lehrbuch der organischen Chemie. Leipzig: Veit.
  19. Knodler, L. A., Edwards, M. R. & Schofield, P. J. (1994). The intracellular amino acid pools of Giardia intestinalis, Trichomonas vaginalis and Crithidia luciliae. Exp Parasitol 79, 117-125.[CrossRef] [Google Scholar]
  20. Kulda, J. & Nohynková, E. (1978). Flagellates of the human intestine and of the intestines of other species. In Parasitic Protozoa , pp. 2-127. Edited by J. P. Kreier. New York:Academic Press.
  21. Liao, J. C., Hoffman, N. E., Barboriak, J. J. & Roth, D. A. (1977). High-performance liquid chromatography of pyruvic and alpha-ketoglutaric acids and its application to urine samples. Clin Chem 23, 802-805. [Google Scholar]
  22. Lloyd, D., Boveris, A., Reiter, R., Filipkowski, M. & Chance, B. (1979). Chemiluminescence of Acanthamoeba castellanii.Biochem J 184, 149-156. [Google Scholar]
  23. Lloyd, D., James, C. J. & Hastings, J. W. (1985). Oxygen affinities of the bioluminescence systems of various species of luminous bacteria. J Gen Microbiol 131, 2137-2140. [Google Scholar]
  24. Lloyd, D., Harris, J. C., Maroulis, S., Biagini, G. A., Wadley, R. B., Turner, M. P. & Edwards, M. R. (2000). The microaerophilic flagellate Giardia intestinalis: oxygen and its reaction products collapse membrane potential and cause cytotoxicity. Microbiology 146, 3109-3118. [Google Scholar]
  25. Mertens, E. (1990). Occurrence of pyrophosphate:fructose 6-phosphate 1-phosphotransferase in Giardia lamblia trophozoites. Mol Biochem Parasitol 40, 147-149.[CrossRef] [Google Scholar]
  26. Paget, T. A., Kelly, M. L., Jarroll, E. L., Lindmark, D. G. & Lloyd, D. (1993a). The effects of oxygen on fermentation in Giardia lamblia. Mol Biochem Parasitol 57, 65-72.[CrossRef] [Google Scholar]
  27. Paget, T. A., Manning, P. & Jarroll, E. L. (1993b). Oxygen uptake in cysts and trophozoites of Giardia lamblia. J Euk Microbiol 40, 246-250.[CrossRef] [Google Scholar]
  28. Phillips, N. F. B., Li, Z. & Lindmark, D. G. (1997). Isolation of a pyrophosphate-dependent phosphofructokinase from Hexamita inflata. Mol Biochem Parasitol 90, 377-380.[CrossRef] [Google Scholar]
  29. Schofield, P. J., Costello, M., Edwards, M. R. & O’Sullivan, W. J. (1990). The arginine dihydrolase pathway is present in Giardia intestinalis. Int J Parasitol 20, 697-699.[CrossRef] [Google Scholar]
  30. Thompson, R. C. A., Reynoldson, J. A. & Mendis, A. H. W. (1993).Giardia and giardiasis. Adv Parasitol 32, 71-160. [Google Scholar]
  31. Townson, S. M., Hanson, G. R., Upcroft, J. A. & Upcroft, P. (1996). Characterisation and purification of pyruvate:ferredoxin oxidoreductase from Giardia duodenalis. Mol Biochem Parasitol 79, 183-193.[CrossRef] [Google Scholar]
  32. Wilhelm, E. R., Battino, R. & Wilcock, R. J. (1977). Low pressure solubility of gases in liquid water. Chem Rev 77, 219-262.[CrossRef] [Google Scholar]

Data & Media loading...

This is a required field
Please enter a valid email address
Approval was a Success
Invalid data
An Error Occurred
Approval was partially successful, following selected items could not be processed due to error