THE EFFECT OF TEMPERATURE ON THE KINETIC PROPERTIES OF PHOSPHOFRUCTOKINASE AND HEXOKINASE FROM THE ANTARCTIC FISH TREMATOMUS BERNACCHII (15th Symposium on Polar Biology)

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Phosphofructokinase (PFK) and hexokinase (HK) were concentrated by ammonium sulfate precipitation from the Trematomus bernacchii's epaxial and cardiac muscles respectively. The apparent Km of PFK for ATP and F6P was established at pH 8.0, at four different temperatures: 5°, 11°, 20° and 30℃. No significant effect of the temperature on the enzyme activity was observed, due to the fact that PFK does not exhibit allosteric properties at pH 8.0. However, at pH 7.0, in which condition the allosteric properties of PFK are displayed, it was observed that the rate of inhibition of the enzyme by ATP at 5℃ is lower than at 20℃. Kinetic data of the allosteric behavior of PFK at pH 7.0, were assayed at 5° and 20℃ in the presence of fixed concentrations of ATP and variable concentrations of F6P. According to the results obtained it was possible to conclude that the enzyme affinity with the substrate was 20 times higher at 5℃ than at 20℃. This result seems to possess high significance in regard to the mechanisms of biochemical adaptation of those organisms at low temperatures. Values for energy of activation for both PFK and HK were also established. The apparent KM for HK from the cardiac muscle was equal to 384μM and 599μM at 5℃ and 20℃, respectively.
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