Protein turnover in skeletal muscle of piglets

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Abstract
1. Rates of protein synthesis and catabolism were measured in longissimus dorsi and hind-limb muscles of suckling piglets.2. Half-lives for synthesis and catabolism for mixed sarcoplasmic proteins were 4.8 and 9.4 d respectively. The corresponding values for mixed myofibrillar proteins were 5.7 and 16.4 d.3. The half-lives for synthesis of sarcoplasmic proteins were significantly different from those of myofibrillar proteins and were not confounded by contamination of the sarcoplasmic protein fraction with plasma proteins of higher specific activity.4. Individual myofibrillar proteins were synthesized and catabolized at rates which were not statistically significantly different. Intramuscular connective tissue also appeared to turnover rapidly, the half-life for synthesis being 8 d and that for catabolism 20 d.5. Values obtained for the specific radioactivities of aspartate + glutamate in mixed plasma proteins support the view that, in so far as the young of animals larger in mature body size than rats or mice are concerned, muscle assumes a more important role relative to liver in regulating whole body amino acid metabolism.