Discontinuities in the arrhenius plots of mitochondrial membrane-bound enzyme systems from a poikilotherm: Acclimation temperature of carp affects transition temperatures

Abstract

1. Evidence is presented for ‘breaks’ in the Arrhenius plots of succinate and cytochrome oxidase systems of mitochondria from carp liver and red epaxial muscle. 2. Arrhenius activation energies (Ea) of succinate and cytochrome oxidase systems above and below the transition temperatures (T*) are about half those reported for homoiotherms (Table 3). Succinate oxidase and cytochrome oxidase obey Michaelis-Menten kinetics. The Km-values for succinate and tetramethyl-p-phenylenediamine (TMPD) (25°C) are similar to those in homoiotherms; they are not affected by acclimation temperature (Table 2). 3. The change inEa of carp liver mitochondria (C.L.M.) occurs at low (high) experimental temperatures if carps are acclimated to low (high) ambient temperatures for at least 4 (3) weeks prior to the experiments (Fig. 1). 4. TheT* shift in Arrhenius plots following a change in acclimation temperature has been studied for succinate oxidation by carp liver mitochondria (Fig. 2). The time constant ofT* change was calculated as taccl.1/2=4.3 days (Fig. 3). Based on the concept of lipid protein interaction the acclimation temperature dependency ofT* is discussed as a possible consequence of a lipid adaptation. 5. Carp acclimated to 26°C and 10°C do not differ significantly with respect to specific activity of liver succinate oxidase determined at 25°C (Table 1). The same is true for the liver-somatic index and the amount of mitochondrial protein per gram of liver (Table 1). Changes, however, are observed in these parameters if carp are in a transitory state of temperature acclimation (early after changing from 26°C to 10°C; Table 1). 6. A bimodal action of temperature change during the process of acclimation is discussed combining the results in a model of succinate oxidase system of carp liver (Fig. 4).