Temporal changes in enzyme activity and mRNA levels during thermal challenge in white sucker

In the early phases of warm acclimation in white sucker Castotomus commersoni, white muscle lactate and succinate, two endproducts of anaerobic energy metabolism, remained unchanged, indicating that energetic imbalance is not a prerequisite for alterations in enzyme levels. The changes in enzyme activities did not correlate with changes in mRNA levels, which argues against transcriptional regulation of enzyme expression under these conditions. The observed induction of cytosolic heat shock protein 70 suggests that the early phases of acclimation to strongly increased temperatures are dominated by enhanced protein degradation, leading to a new balance between synthesis and degradation and, therefore, new steady-state enzyme concentrations. Copyright 2000 The Fisheries Society of the British Isles