Lactate content and lactate dehydrogenase activity inPalaemon serratus abdominal muscle during temperature changes

Summary

Lactate concentration was measured in the abdominal muscle of the shrimpPalaemon serratus. Rapid and seasonal temperature changes result in an increase of the lactate content of approximately 3–4 fold.

Lactate dehydrogenase from the abdominal muscle exhibits a temperature dependent pyruvate inhibition with pyruvate as substrate.

The kinetic parameters of lactate dehydrogenase fromPalaemon serratus are found to vary during rapid temperature changes: V_max increases with temperature from 0.06 μmol min⁻¹ (mg protein)⁻¹ at 10°C to 0.28 μmol min⁻¹ (mg protein)⁻¹ at 30°C with lactate as substrate, and from 5.5 μmol min⁻¹ (mg protein)⁻¹ at 10°C to 26.2 μmol min⁻¹ (mg protein)⁻¹ at 30°C, with pyruvate (Table 1). The Hill coefficientn _H, decreases with temperature from 2.2 to 1.2 when the pyruvate reduction is examined, but remains near 1.2 when the activity is measured with lactate as substrate (Table 1). The S_0.5 values for lactate show a tendency to increase below 30 °C (18.9 mM l⁻¹ at 20 °C) whereas the S_0.5 for pyruvate is found to increase greatly with temperature (0.004 mM l⁻¹ at 10 °C and 0.06 mM l⁻¹ at 20 °C).

Long term temperature changes involve variations of lactate dehydrogenase activity leading to inverse thermal compensation (Table 2).

Activation energy (about 56 kJ both with pyruvate and lactate) does not vary during the year, suggesting that temperature adaptation does not induce important catalytic changes (Table 3).