Leucine increases the inhibitory effect of insulin on protein degradation in C2C12 myotubes. Fully differentiated myotubes were pre labelled with L[ring -3, 5-3H]-tyrosine for 48 hours. Myotubes were rinsed twice with 1 × HBS and chased in 0.2 × PC AA medium for 2 hours followed by incubation with 30 (filled bars), 150 (open bars) and 750 (hatched bars) μM leucine in 0.2 × PC AA medium. Values are means ± SEM for two experiments performed in quadruplets. * Represents significant differences among leucine levels whereas ψ indicates differences relative to control groups.