Short-term responses of protein synthesis to re-feeding in rainbow trout

Abstract

Protein synthesis was measured in various tissues of rainbow trout which had been fasted for 6 days and re-fed in one meal. After re-feeding, tissue fractional rates of protein synthesis ( k s, %/day) were significantly increased by 3 h after the meal, with the exception of the white muscle which increased after 6 h. These changes in protein synthesis did not involve any alteration in the RNA to protein ratio (i.e., tissue ribosome concentration) and were brought about through an increase in the amount of protein synthesis per unit RNA (g protein g RNA −1 day; k s RNA ). Liver k s was resistant to the 6-day fast, therefore the stimulation by re-feeding was transient in nature. Further evidence was obtained to show that this stimulation in liver k s was very rapid, occurring after 1 h. Sub-cellular fractionation of the liver showed that there were differences in k s between the nuclear, mitochondrial and post-mitochondrial supernatant fractions. One hour after re-feeding, there was a preferential stimulation in both the fractional rate of protein synthesis and total amount of protein synthesis in the mitochondrial fraction which returned more rapidly towards levels in fasted fish than did the nuclear and post-mitochondrial fractions.