Biochemical Studies on Myofibrils of Fish

Thermo-stability of Ca²⁺-activated Myofibrillar ATPase of Epipelagic and Mesopelagic Fish Species

Abstract

The thermo-stability of myofibrils prepared from dorsal muscles of epipelagic and mesopelagic fish species was studied.
1. The rate constant, KD of inactivation of myofibrillar Ca²⁺-ATPase activity based on the first order reactions at 25°C, 30°C, and 35°C varied markedly among fish species.
2. The order of thermo-stability, from the most stable to the least, of the myofibrillar Ca²⁺-ATPase in epipelagic fish studied was: tilapia, seabass, yellowfin tuna, carp, yellowtail, red sea bream, shark, rainbow-trout, Pacific mackerel, conger eel, Japanese rockfish, American plaice, Pacific cod, and atka mackerel.
3. The myofibrillar Ca²⁺-ATPase from mesopelagic fish species was more unstable against temperature than that from epipelagic fish species.
4. It is, therefore, presumed that the thermo-stability of myofibrillar Ca²⁺-ATPase of a fish has adapted to the respective body temperature or environmental temperature at which the fish lived.
5. With regards to Ca²⁺-ATPase, the relative order of thermo-stability of myofibrils of the fishes coincided with the previously reported order of their actomyosins.
6. The myofibrils from two carp specimens, cultured at 3°C and 28°C, showed little difference in KD values, in contrast with the striking difference of environmental temperatures.It was, however, found that the gradients of the Arrhenius plots for Ca²⁺-ATPase were clearly different for the two preparations.