High activity antioxidant enzymes protect flying-fox haemoglobin against damage: an evolutionary adaptation for flight?
Flying-foxes are better able to defend haemoglobin against autoxidation than non-volant mammals such as sheep. When challenged with the common physiological oxidant, hydrogen peroxide, haemolysates of flying-fox red blood cells (RBC) were far less susceptible to methaemoglobin formation than sheep. Challenge with 1-acetyl-2-phenylhydrazine (APH) caused only half as much methaemoglobin formation in flying-fox as in ovine haemolysates. When intact cells were challenged with phenazine methosulfate (PMS), flying-fox RBC partially reversed the oxidant damage, and reduced methaemoglobin from 40 to 20% over 2 h incubation, while ovine methaemoglobin remained at 40%. This reflected flying-fox cells' capacity to replenish GSH fast enough that it did not deplete beyond 50%, while ovine RBC GSH was depleted to around 20%. The greater capacity of flying-foxes to defend haemoglobin against oxidant damage may be explained in part by antioxidant enzymes catalase, superoxide dismutase and cytochrome-b ( 5 ) reductase having two- to four-fold higher activity than in sheep (P < 0.001). Further, their capacity to limit GSH depletion to 50% and reduce methaemoglobin (in the presence of glucose), despite ongoing exposure to PMS may result from having ten-fold higher activity of G6PD and 6PGD than sheep (P < 0.001), indicating the presence of a very efficient pentose phosphate pathway in flying-foxes.
Reinke
N B
NB
School of Biological, Biomedical and Molecular Sciences, University of New England, Armidale, NSW, 2351, Australia.
O'Brien
G M
GM
D000222:Adaptation, Physiological / Q000502:physiology; D000818:Animals; D000975:Antioxidants / Q000378:metabolism; D002374:Catalase / Q000378:metabolism; D002685:Chiroptera / Q000378:metabolism*; D042966:Cytochrome-B(5) Reductase / Q000378:metabolism; D004912:Erythrocytes / Q000201:enzymology*; D005426:Flight, Animal / Q000502:physiology*; D005954:Glucosephosphate Dehydrogenase / Q000378:metabolism; D005978:Glutathione / Q000378:metabolism; D005982:Glutathione Transferase / Q000378:metabolism; D008706:Methemoglobin / Q000378:metabolism; D010734:Phosphogluconate Dehydrogenase / Q000378:metabolism; D012756:Sheep / Q000378:metabolism*; D013482:Superoxide Dismutase / Q000378:metabolism
D000975:Antioxidants; D008706:Methemoglobin; D010734:Phosphogluconate Dehydrogenase; D005954:Glucosephosphate Dehydrogenase; D002374:Catalase; D013482:Superoxide Dismutase; D042966:Cytochrome-B(5) Reductase; D005982:Glutathione Transferase; D005978:Glutathione