- In fall and winter, the liver of the winter flounder produces large amounts of alanine-rich (60 mol %) antifreeze proteins for export to the circulation. We have examined the tRNA in the liver to see if the seasonal production of antifreeze protein is accompanied by changes in tRNAAla isoacceptors. Total tRNA from the liver of winter fish showed an approximate 40% increase in alanine acceptor capacity over tRNA from summer fish. In contrast, the acceptor capacities for other amino acids showed no seasonal difference. When labeled alanyl-tRNAs were separated by reverse phase chromatography-5 chromatography, a large proportion of the increase in alanine acceptor capacity was in one of three main peaks. Measurements of the optimum temperatures for various flounder amino-acyl-tRNA synthetases suggest that alanyl-tRNA synthetase functions best between 0 and 5 degrees C, which is the sea water temperature when antifreeze protein synthesis occurs, while prolyl- and valyl-tRNA synthetases are most active between 20 and 30 degrees C. These differences in temperature optima and the seasonal variation in tRNAAla levels and isoaccepting species may both serve to optimize antifreeze protein production by increasing the translational efficiency of its mRNA.