Effect of acclimation temperature on the elongation step of protein synthesis in different organs of rainbow trout.

Cytosolic extracts of liver, kidney, spleen, gill, red and white muscle from rainbow trout acclimated to 4 and 17 degrees C, respectively, have been investigated in vitro with respect to their enzymic activity in stimulating the growth of nascent peptide chains (labelled polyphenylalanine) at assay temperatures from 5 to 25 degrees C using polyuracil as messenger RNA. The elongation step of protein synthesis is characterized by a Q10 value of about 2.4 (range 10-25 degrees C) in all organs from both, 4 and 17 degrees C acclimated fish. Except for the red muscle, the organs of cold acclimated trout, however, exhibit significantly higher specific elongation rates (mol phenylalanine polymerized/(g wet weight X h)) at any experimental temperature than those of warm acclimated fish. This increase of the elongation rates varies between the organs and ranges from +29% (liver) to +60% in the gill. The specific acylation rate (mol phenylalanyl-tRNA formed/(g wet weight X h] surpasses the specific elongation rate by a factor of at least 8.5. Moreover, the specific acylation rate per mg protein is independent of acclimation temperature. It is concluded that the increased specific elongation rates in 4 degrees C acclimated trout are not due to altered pool sizes of the precursor phenylalanyl-tRNA, but reflect an effective enhancement of enzymic elongation factor activities. In accordance with data taken from literature, this finding suggests a compensatory enhancement of in vivo protein synthesis to occur in trout during cold acclimation.