Mitochondrial enzymes of tropical fish: a comparison with fish from cold-waters

Abstract

1. 1. Mitochondria from heart and liver of the following species of tropical fish were isolated: Plectropoma maculatum, Lethrinus chrysostomus, Acanthrus xanthopterus and Mugil cephalus. 2. 2. The fatty acid composition of the tropical fish mitochondrial membranes was found to be more saturated than in previously reported cold-water fish motochondrial membranes. 3. 3. Temperature effects were observed on the membrane-associated enzymes succinate oxidase and succinate dehydrogenase and compared with the matrix-associated malate dehydrogenase. The membrane-associated system was characterized by a sharp temperature profile in comparison with the broader profile for the matrix enzyme. 4. 4. All enzyme activities were higher in the heart than liver mitochondria. The heart mitochondrial enzymes were also more temperature-stable than the corresponding enzymes of the liver. 5. 5. Linear Arrhenius plots below about 20–25°C were recorded for all enzymes. However, departures from linearity were observed above these temperatures in the case of membrane-associated enzymes. 6. 6. Activation energies for succinate oxidase in the temperature ranges 5–25 and 25–40°C were between 65–120 and 25–55 kJ mol −1 respectively. 7. 7. The results are discussed in relation to the physiological significance of linear and non-linear Arrhenius plots in poikilothermic and homeothermic animals.