Adaptations in Mg 2+ ‐activated myofibrillar ATPase activity induced by temperature acclimation

Early work on myosin isolated from North Sea fish showed the molecule to be peculiarly unstable relative to corresponding preparations from homoiothermic animals [ 1,2]. The tendency for fish myosin preparations to form aggregated products together with its thermal lability and rapid loss of activity on storage have made studies of the ATPase activity difficult [3]. In contrast to myosin preparations myofibrils isolated from cold water fish have been shown to be relatively more stable allowing accurate and meaningful studies of the ATPase to be carried out [4]. Studies of temperature adaptation of the Mg*‘-activated myofibrillar ATPase between different species have shown there to be a strong positive correlation between thermostability and environmental temperature IS]. The myofibrillar ATPase activity of fish adapted to low environmental temperatures has been found to be relatively higher at low temperatures than homologous preparations from warm adapted species [5,6]. As with certain other enzyme systems [7,8] the apparent energy of activation was found to be positively correlated with the adaptation temperature of the species [5.6]. While most species are restricted to quite a narrow thermal tolerance range a few fish species, such as the goldfish (Curassius auru~us L.), are able to survive almost the whole range of physiological temperatures. In this present paper the properties of white muscle myofibrils from goldfish acclimated to 1°C and 26°C has been studied. Evidence has been obtained for