Biochemical Adaptation to the Environment

SYNOPSIS. Biochemical adaptation to environmental parameters such as temperature appears to involve two distinct types of changes in the organism's chemistry. On the one hand, the quantities of certain molecular species present in the cells may change. Alternatively, the actual types of molecules present may vary. Rainbow trout (Salmo gairdneri) acclimated to warm and cold temperatures exhibit a striking example of this latter type of adaptation. For all enzymes we have examined in this species, distinct “warm” and “cold” isozymes are present. The isozymes found in warmacclimated (18°C) trout function well only at temperatures above 10–12°C. The isozymes present in cold-acclimated (4°C) trout function optimally at 2-5°C, temperatures this species normally encounters in winter. These data, plus information on comparable changes in membrane lipids, lead us to propose that adult poikilotherms may undergo a considerable degree of “biochemical restructuring” on a seasonal basis. The factors which control this “restructuring,” and the rates at which the process occurs at high and low temperatures, are topics for future investigation.