Journal: Journal of Nutrition. February 2007;137:357-362
Authors and affiliation: Anthony TG, McDaniel BJ, Knoll P, Bunpo P, Paul GL, McNurlan MA. Department of Biochemistry and Molecular Biology, Indiana University School of Medicine-Evansville, Evansville, Indiana. [E-mail: firstname.lastname@example.org]
The purpose of this investigation was to compare the early response of skeletal muscle protein synthesis and translation initiation following the ingestion of different protein sources after endurance exercise.
Treadmill-acclimated rats were designated as either non-exercised controls (NEX) or treadmill exercised for 2 hours at 26 m/min (approximately 75% VO2max) and then fed either carbohydrate only (EC), carbohydrate plus soy protein (ES), or carbohydrate plus whey protein (EW).
One hour after exercise, serum insulin concentrations in EC, ES, and EW were greater than in NEX (P<0.05); the concentration in EW was greater than in EC, with that in ES intermediate. Serum concentrations of branched-chain amino acids in ES and EW were higher than in EC, but serum leucine and isoleucine in EW were higher than in ES (P<0.05).
Nevertheless, both soy protein and whey protein promoted the fractional rate of skeletal muscle protein synthesis significantly more than carbohydrate only. Likewise, compared with EC, both ES and EW increased formation of the mRNA cap binding complex eIF4F and stimulated phosphorylation of the translational repressor, 4E-BP1, the 70kD ribosomal protein S6 kinase (S6K1), and the mammalian target of rapamycin (mTOR) kinase at serine 2448. On the other hand, phosphorylation of S6K1 and mTOR was greater in EW than in ES (P<0.05).
In conclusion, general protein synthesis and the mRNA cap binding step are promoted comparably by soy protein and whey protein in the skeletal muscle of exercised rats. Furthermore, the data suggest that mTOR signaling in skeletal muscle is acutely responsive to physiological variations in dietary amino acids.