Evolutionary temperature adaptation of fish sarcoplasmic reticulum |
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Authors: | Harry J McArdle and Ian A Johnston |
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Institution: | (1) Department of Physiology, University of St. Andrews, St. Andrews, Fife, UK |
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Abstract: | Summary Sarcoplasmic reticulum has been isolated from the white muscle of 15 species of teleost fish adapted to diverse thermal environments. Evidence has been obtained that the Ca2+-dependent ATPase of fish sarcoplasmic reticulum has undergone evolutionary modification for function at different temperatures. Compared with tropical fish, cold adapted species have higher rates of Ca2+ transport and Ca2+-ATPase activities at low temperatures. Most species have linear Arrhenius plots over the temperature range 0–30°C. Activation enthalpies ( H
) of the ATPase ranged from 53–190 kJ mol–1 and were positively correlated with environment temperature. Activation entropy ( S
) varied from negative values in cold adapted species to positive values in tropical fish.In contrast to the Ca2+-ATPase, the basal ATPase of fish sarcoplasmic reticulum showed no relationship between either ATPase activity or thermodynamic activation parameters and environmental temperature.Only the Ca2+-dependent ATPase is coupled to Ca2+ transport. The percentage of total ATPase activity which is Ca2+ activated is higher at low temperatures in cold than in warm adapted species. For example, ratios of Ca2+-dependent/total ATPase at 2°C varied from 80–98% in Arctic, Antarctic and North Sea species to only 2–50% in various tropical fish. Above 20°C, similar ratios in the range 80–98% were obtained for all species. The nature of the basal ATPase and mechanisms of temperature adaptation of fish sarcoplasmic reticulum are discussed.Abbreviations
ET
environmental temperature
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EGTA
ethylene glycol-bis ( -aminolethyl ether)-N, N -tetraacetic acid
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HEPES
N-2-hydroxylpiperazine-N -2-ethanesulfonic acid
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SR
sarcoplasmic reticulum |
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