It is widely believed that enzymatic activities in ectothermic organisms adapt to environmental temperatures. However, to date, no study has thoroughly compared multiple thermodynamic enzymatic characteristics across species living in dramatically different environments. To start to address this gap, we compared the characteristics of lactate dehydrogenase (LDH) purified from the muscles from slime flounder Microstomus achne white muscle and bovine skeletal muscle (bM4) and heart. The K m and V max for pyruvate reduction were about three times higher for M. achne LDH than bM4 Surprisingly, maximum LDH activity was observed at ∼30 °C and ∼50 °C for M. achne and bovine LDHs, respectively, suggesting that the maximum enzymatic activity of LDH is set at a temperature ∼20 °C higher than environmental or body temperature across species. Although K m and V max values of these LDHs increased with temperature, the V max/K m ratio for M. achne LDH and bM4 was independent. Differential scanning calorimetry and enthalpy change measurements confirmed that M. achne and bovine muscle-specific LDHs shared similar properties. Based on the present findings and previous reports, we hypothesize that the function and thermodynamic properties of muscle LDH are highly conserved between a teleost adapted to cold, M. achne, and bovine.
Keywords: ectothermy; endothermy; heat capacity; kinetics; lactate dehydrogenase; temperature.
© The Authors 2016. Published by Oxford University Press on behalf of the Japanese Biochemical Society. All rights reserved.