COMPENSATION OF LIVER PROTEIN SYNTHESIS IN TEMPERATURE-ACCLIMATED TOADFISH, OPSANUS TAU

Liver protein synthesis was measured with a rapid arterial injection procedure in control (20-23°) and cold-acclimated (10°) toadfish. The results were expressed as the cpm of radioactive amino acids incorporated into protein compared to cpm of free radioactivity in the liver homogenate, to correct for variability in injections and in uptake of amino acids by the liver. The results show that, when measured at 20-23°, the 10° acclimated fish possess liver protein synthetic capacity about 75% greater than fish maintained at the higher temperature. Two series of experiments, in which fish were maintained in running sea water aquaria or in static artificial sea water aquaria, gave comparable results. The livers were analyzed for DNA, RNA, protein and free amino acids. The levels of these constituents resembled those in mammalian liver with the exception of RNA, which was lower. Under the conditions of these experiments no significant changes were observed in the constituents measured as a result of two-week cold acclimation. The possibility of a common translational-type control over protein synthesis to account for increased enzyme levels in cold temperature acclimation is discussed.