In vivo protein synthesis in different tissues and the whole body of rainbow trout (Salmo gairdnerii R.). Influence of environmental temperature.

The fractional protein synthesis rate (FSR) of tissue (liver, digestive tract, muscle and whole fish) proteins was measured in rainbow trout acclimated to 9 and 18 degrees C after a pulse injection of [U-14C] L-leucine. In each of the tissues two FSRs were calculated based on a different estimate of the specific radioactivity of leucine in the precursor compartment for protein synthesis. Whole fish protein synthesis (WFPS) was estimated to be 7 and 7.6 g protein per kg body weight and per day respectively at 10 and 18 degrees C. Muscle and digestive tract contributed the most (more than 30%) to WFPS. The rate of protein turnover in whole fish was very low, as in the muscle, when compared to liver and digestive tract.