Quantitative protein synthetic rates in various tissues of a temperate fish in vivo by the method of phenylalanine swamping.

1. A single high-dose injection of 14C- (or 3H-) phenylalanine was used for measurement of protein synthetic rates in tissues of toadfish, Opsanus tau, in vivo. 2. Average rates at 20 degrees C, as per cent of tissue protein synthesized per day, were as follows: liver, 14; head kidney, 15; gill, 7.7; spleen 5.0; heart, 2.3; testis, 1.4; epaxial and pectoral muscle, 0.20-0.23. Elevated rates in muscle (0.71%/day) were found in fed fish. 3. Temperature dependency (Q10) in the 10-20 degrees C range averaged 6-7 for tissues with high rates of protein turnover, and 3-4 in heart and muscle after two-weeks acclimation.