Protein synthesis in liver, muscle and gill of mullet (Mugil cephalus L.) in vivo.

1. Protein synthesis in mullet was measured by use of pulse injections of 14Cleucine into the hepatic portal circulation and by 4-hr continuous infusion of 14Ctyrosine into the dorsal aorta. 2. Liver protein synthesis was 37 mg/day per g wet weight of tissue. Plasma proteins accounted for about 25% of total liver protein synthesis. Replacement rate for intrahepatic proteins was 20%/day. Average polypeptide chain synthesis time was 3 min. 3. Gill protein synthesis was comparable to that in liver with a replacement rate of 23%/day. 4. Muscle protein synthetic rate was 0.54%/day, comparable to rates in rabbit and sheep when temperature difference is taken into account. 5. Constant infusion is shown to be a feasible technique for measurement of protein metabolism of fish in vivo.