Fig. 1. Effects of temperature and cadmium exposure on activity of upstream complexes of mitochondrial electron transfer chain (Complexes I and II) in oyster gills and hepatopancreas (HP). Activity presented as units (μmol product min^− 1) per g cellular protein. Asterisks represent values significantly different from the respective controls in the absence of Cd (Dunnett's test, P <0.05) (top row of asterisks correspond to the values measured at 30 °C, and bottom row—at 20 °C, respectively). Trend lines were obtained by second order polynomial smoothing. Vertical lines represent standard errors; the absence of vertical lines means that the standard error is smaller than symbol size. N=5–8.

Fig. 2. Effects of temperature and cadmium exposure on activity of downstream complexes of mitochondrial electron transfer chain (Complexes III and IV) in oyster gills and hepatopancreas (HP). Activity presented as units (μmol product min^− 1) per g cellular protein. Asterisks represent values significantly different from the respective controls in the absence of Cd (Dunnett's test, P < 0.05). Trend lines were obtained by second order polynomial smoothing. Vertical lines represent standard errors; the absence of vertical lines means that the standard error is smaller than symbol size. N = 5.

Fig. 3. Effects of temperature and cadmium exposure on activity of key Krebs cycle enzymes (CS and NAD-IDH) and NADP-IDH in oyster gills and hepatopancreas (HP). Activity presented as units (μmol product min^− 1) per g cellular (for CS) or mitochondrial (for NAD- and NADP-IDH) protein. Asterisks represent values significantly different from the respective controls in the absence of Cd (Dunnett's test, P < 0.05). Trend lines were obtained by second order polynomial smoothing. Vertical lines represent standard errors; the absence of vertical lines means that the standard error is smaller than symbol size. N = 4–6.

Fig. 4. Activation energy (Ea, kJ mole⁻¹) of key mitochondrial enzyme complexes from gills and hepatopancreas of eastern oysters Crassostrea virginica. Ea were determined in the range 20–30 °C. Trend lines were obtained by second order polynomial smoothing.

Fig. 5. Activation energy (Ea, kJ mole^− 1) of mitochondrial matrix enzymes from gills and hepatopancreas of eastern oysters Crassostrea virginica. Ea were determined in the range 15–25 °C. Trend lines were obtained by second order polynomial smoothing.

ANOVA: Effect of cadmium exposure, temperature and cadmium-temperature interactions on activity of key mitochondrial enzymes in eastern oysters Crassostrea virginica

F values with degrees of freedom for the effect and the error (in brackets) and probability values (P) are given; significant effects are highlighted in bold. Concentration of Cd ranged from 0 to 400 μM. Temperature was 20 °C and 30 °C for ETC complexes, and 15 °C and 25 °C for CS and NAD-IDH, NADP-IDH.

Apparent inhibition constants for Cd (IC₅₀, μM) of key mitochondrial enzymes from eastern oysters Crassostrea virginica

Cd effects were determined in the range 0–400 μM at 20 and 30 °C for ETC enzymes and 15° and 25 °C for Krebs cycle enzymes and NADP-IDH. Square brackets indicate extrapolated IC₅₀ values for the cases when 50% inhibition could not be achieved even at the highest studied Cd level (400 μM). N.D.—not determined.