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First published online December 14, 2006
Journal of Experimental Biology 210, 46-55 (2007)
Published by The Company of Biologists 2007
doi: 10.1242/jeb.02589
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Temperature-dependent effects of cadmium and purine nucleotides on mitochondrial aconitase from a marine ectotherm, Crassostrea virginica: a role of temperature in oxidative stress and allosteric enzyme regulation

Anton A. Cherkasov, Robert A. Overton, Jr, Eugene P. Sokolov and Inna M. Sokolova*

Biology Department, University of North Carolina at Charlotte, 9201 University City Boulevard, Charlotte, NC 28223, USA


Figure 1
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  		Fig. 1. Cadmium-induced ROS production in oyster mitochondria. (A) Total rate of ROS production in control mitochondria and those exposed to 50 µmol l-1 Cd at 20°C. (B) Percentage oxygen converted to ROS in oyster mitochondria, which was calculated by dividing the rate of ROS production by the rate of mitochondrial oxygen consumption measured with the same substrates at 20°C. ROS production and MO2 of complete and partial ETC was measured with complex-specific substrates as described in `Materials and methods'. *Values significantly different from the respective controls (P<0.05). Values are means ± s.e.m., N=5-7.

 

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  		Fig. 2. Effects of Cd exposure on aconitase activity in intact (A) and permeabilized (B) mitochondria of oysters Crassostrea virginica. Cd was either incubated with intact mitochondria (A), or directly added to Triton X-100 permeabilized mitochondria (B). *Values significantly different from the respective controls (P<0.05). Aconitase activity in B is presented as a percentage of the respective control values. Cd added to permeabilized mitochondria had no effect on aconitase activity (P>0.28). N=5-11, except for 10 µmol l-1 and 75 µmol l-1 Cd (N=3-4).

 

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  		Fig. 3. Expression of mRNA of mitochondrial uncoupling proteins in gill tissues of Crassostrea virginica. Lanes 1 and 8: DNA size markers; lanes 2 and 5: UCP4; lanes 3 and 6: UCP5; lanes 4 and 7: UCP6. Samples in lanes 2-4 and 5-7 were mRNA isolated from two individual oysters, respectively.

 

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  		Fig. 4. Effects of purine nucleotides on aconitase activity in oyster mitochondria. (A) ATP, (B) ADP and (C) GDP. Total nucleotide concentrations are given, and aconitase activity is expressed as a percentage of the respective control values. *Values significantly different from the controls (P<0.05). N=3-9, except for 10 mmol l-1 ATP (N=2).

 

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  		Fig. 5. Uncoupling protein (UCP) involvement in antioxidant protection of aconitase activity in oyster mitochondria. (A) GDP (3.5 mmol l-1) was incubated with intact mitochondria and either removed by washing in nucleotide-free buffer (+wash) or left in the assay medium (-wash) prior to the determination of aconitase activity. *Value significantly different from the respective controls (P<0.05). (B) Mitochondria were incubated with GDP (3.5 mmol l-1), oleate (5 µmol l-1) and/or Cd (200 µmol l-1) and washed to remove the additives prior to the measurements of aconitase activity. *Values significantly different from the respective controls (no Cd; P<0.05). aValue significantly different from the Cd only value at the respective temperature (P<0.05). Values are means ± s.e.m.; N=3 (A), N=5 (B).

 




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