The effect of temperature on catalytic and regulatory functions of pyruvate kinases of the rainbow trout and the Antarctic fish Trematomus bernacchii

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Abstract
1. The effects of temperature on the catalytic and regulatory properties of pyruvate kinases from the temperate-zone rainbow trout and the Antarctic fish Trematomus bernacchii were examined. 2. The Km value of pyruvate kinase for one of its two substrates, phosphoenolpyruvate, is temperature-dependent, and is lowest at temperatures that closely coincide with the habitat temperatures of the two fishes. 3. Two regulatory functions of pyruvate kinase, feedforward activation by fructose diphosphate and feedback inhibition by ATP, are temperature-independent. Enzyme–ADP interaction is also temperature-independent. 4. It is concluded that enzyme–substrate and enzyme–modulator interactions are important factors in short-term and in evolutionary adaptations by poikilotherms to changes in temperature. Though the Km for substrate may vary in apparently adaptive manners, the regulatory functions of an enzyme appear to be unchanged over the range of temperatures experienced by the organism in Nature.