Temperature and Ca 2+-dependence of the sarcoplasmic reticulum Ca 2+-ATPase in haddock, salmon, rainbow trout and zebra cichlid

Abstract

Temperature dependence of Ca 2+-ATPase from the sarcoplasmic reticulum (SR) in rabbit muscle has been widely studied, and it is generally accepted that a break point in Arrhenius plot exist at approximately 20 °C. Whether the break point arises as a result of temperature dependent changes in the enzyme or its membrane lipid environment is still a matter of discussion. In this study we compared the temperature dependence and Ca 2+-dependence of SR Ca 2+-ATPase in haddock ( Melanogrammus aeglefinus), salmon ( Salmo salar), rainbow trout ( Oncorhynchus mykiss) and zebra cichlid ( Cichlasoma nigrofasciatum). The Arrhenius plot of zebra cichlid showed a break point at 20 °C, and the haddock Arrhenius plot was non-linear with pronounced changes in slope in the temperature area, 6–14 °C. In Arrhenius plot from both salmon and rainbow trout a plateau exists with an almost constant SR Ca 2+-ATPase activity. The temperature range of the plateau was 14–21 and 18–25 °C in salmon and rainbow trout, respectively. Ca 2+-dependence in the four different fish species investigated was very similar with half maximal activation ( K 0.5) between 0.2 and 0.6 μM and half maximal inhibition ( I 0.5) between 60 and 250 μM. Results indicated that interaction between SR Ca 2+-ATPase and its lipid environment may play an important role for the different Arrhenius plot of the different types of fish species investigated.