Abstract
1. 1. The initial rate of protein synthesis, as measured by the level of incorporation in 1 hr of 14C-leucine into protein, exhibited a compensation in gill and liver of goldfish acclimated at 5°C only when tested at 25°C. However, muscle of 5°C fish showed a greater incorporation than that of 25°C fish at 15°C and 25°C but not at 5°C. The Q 10 of the incorporation rate was higher for the 25°C-acclimated fish than for the 5°C-acclimated ones in the lower range of temperature, but this relationship was reversed in the higher thermal range. 2. 2. All the tissues reached a steady-state level of incorporation within 6–12 hr after the injection of the isotopic precursor in both the cold- and warm-adapted fish, when measured at 15°C. 3. 3. The maximal net synthesis of protein at 12 hr of incorporation was 100–500 per cent higher in the cold-acclimated tissues than in the warm-acclimated ones at 5°C and less so at 15°C. There were no significant differences between the cold- and warm-adapted gill and liver in the net protein synthesis at 25°C, although muscle showed a 50 per cent reduction in this process during warm acclimation. 4. 4. The 14C-count in the PCA-supernatants of the warm-acclimated tissues was higher than in the cold-acclimated, ones, when measured 1 hr after the injection of 14C-leucine at 15°C; this might signify a greater amino acid permeability of the cell membrane during warm acclimation. However, no difference was found in 14C-counts of the PCA-soluble pools of the corresponding tissues from cold- and warm-adapted fish, when measured either at 5° or 25°C, 12 hr after the administration of the isotope. Thus the availability of the precursor did not seem to be rate limiting for the protein synthesis, although a rapid metabolism of the amino acids in the warm-adapted fish tissues cannot be excluded. 5. 5. It is concluded that the translational increase in enzymatic activities and oxidative metabolism of goldfish during cold acclimation may be achieved by a complicated rotational (gill and liver) or a simple translational (muscle) augmentation of the maximal net synthesis of proteins.
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