Effect of leucine-rich dietary protein on in vitro protein synthesis in porcine muscle.

Experiments were conducted to determine the effect of feeding diets containing leucine-rich proteins on in vitro protein synthesis in porcine muscle. Swine (10 kg initial weight) were fed for 4 weeks diets composed mainly of corn gluten meal, corn and soybean meal, and containing a total of 2.00, 2.33, 2.92, 3.12, 3.53, and 4.01% leucine. At the end of the growing period, six swine fed each diet were killed and samples of biceps femoris, longissimus dorsi, and triceps brachii were excised. Incorporation of [14C]phenylalanine into newly synthesized protein was measured using a cell-free in vitro system following recombination of purified soluble protein and ribosomal fractions. The feeding of diets containing increasing amounts of leucine-rich protein increased the free leucine concentration in plasma and skeletal muscle. There was no significant effect of diet on incorporation of [14C]phenylalanine into muscle protein following simple recombination of soluble protein and ribosomal fractions from the same tissues. Combination of muscle soluble protein from animals fed 2.00% leucine with ribosomal fractions of animals fed increasing quantities of leucine-rich protein, however, indicated increased protein synthetic activity of the ribosomal fraction in all muscles tested. Protein synthetic activity of the soluble protein fraction was not affected by diet. It was concluded that the feeding of leucine-rich dietary proteins beyond requirements for maximal rate of growth can increase the protein synthetic potential of porcine muscle cells although whole body growth is depressed.