Mechanisms of temperature acclimation in the channel catfish Ictalurus punctatus: Isozymes and quantitative changes

Abstract

Enzymes from liver and muscle of channel catfish acclimated to 7, 15 or 25°C were analyzed by starch gel electrophoresis and Western blot analysis to examine the roles of isozymes and quantitative changes in enzyme expression during temperature acclimation. No temperature-induced changes in isozyme expression were found for glucose-6-phosphate dehydrogenase (G6PDH), 6-phosphogluconate dehydrogenase, lactate dehydrogenase (LDH) or malate dehydrogenase in either muscle or liver. Relative concentration (Western blot scan intensity normalized to protein or DNA content of tissue homogenate) of liver G6PDH was higher for cold-acclimated fish than for warm-acclimated fish. This trend was consistently seen when 7°C-acclimated fish were compared to 15- and 25°C-acclimated fish and in three of four experiments comparing 15- and 25°C-acclimated fish. Differences in G6PDH concentration paralleled differences in G6PDH activity between the temperature groups. Concentration and activity of LDH showed no consistent trend with respect to acclimation temperature. It is concluded that changes in G6PDH activity associated with temperature acclimation are not the result of qualitative isozyme changes but are due to quantitative changes in the enzyme. LDH, which displays little change in activity during temperature acclimation, does not change significantly in concentration during temperature acclimation.