Thermal modulation of pyruvate metabolism in the freshwater prawn Macrobrachium malcolmsonii: the role of lactate dehydrogenase

Abstract

Temperature-induced alterations in the activity of the enzyme lactate dehydrogenase (LDH) were evaluated in the freshwater prawn Macrobrachium malcolmsonii in three groups of juveniles: controls maintained at 27±2 °C; test prawns exposed to 35 °C; test prawns exposed to 15 °C. Changes in LDH activity and lactate levels in key tissues were assessed after 48 hrs. LDH in the skeletal muscle of the prawns was also subjected to kinetic analysis at different temperatures. Native polyacrylamide gel electrophoresis (PAGE) analysis and colorimetric estimation revealed decreased LDH activity (compared to controls) in the gill, heart and haemolymph, but not in the skeletal muscle or hepatopancreas, of test prawns exposed to 15 °C; however, lactate levels were significantly lower in all the tissues of these test prawns. Conversely, prawns exposed to 35 °C revealed elevated LDH activity in all the tissues, barring the skeletal muscle, while lactate levels were significantly higher (compared to controls) in all the tissues of these prawns. Kinetic analysis of LDH in the skeletal muscle at different assay temperatures revealed temperature-dependent kinetic properties. The differences observed in LDH activity and levels of lactate in various tissues of prawns exposed to low and high temperatures suggest aerobic and anaerobic patterns of pyruvate metabolism at respective temperatures. The results obtained by kinetic analysis of LDH in the skeletal muscle suggest the occurrence of an adaptative response involving this enzyme that enables M. malcolmsonii to cope with effects of thermal stress.