title: Relative roles of polysomes and cytoplasmic enzymes in regulating bovine skeletal muscle protein synthesis.
abstract: Activities of cytoplasmic enzyme or polysomal fractions, both prepared from longissimus muscle of bovine animals differing markedly in muscle growth were measured in cell-free, protein synthesis assays. Two groups of animals were used: 1) eight animals comprising two "double-muscled" animals fed a high-energy diet, two "double-muscled" animals fed a low-energy diet, two "normal" animals fed a high-energy diet and two "normal" animals fed a low-energy diet and 2) six animals differing in age and sex and including two bull calves, 87 and 145 kg; two 18- to 24-mo-old animals, 411 and 596 kg and two cows, 594 and 681 kg. Ability of cell-free, protein-synthesis systems prepared from muscle of different animals to incorporate amino acids into TCA-precipitable protein differed significantly and was in direct correlation with phenotypic muscle growth. Mixing experiments using cytoplasmic enzymes from one set of animals with polysomes from another set showed that source of cytoplasmic enzymes had a greater effect on rate of in vitro protein synthesis than source of polysomes. Cytoplasmic enzymes and polysomes from double-muscled animals and animals fed a high-energy diet supported more rapid in vitro protein synthesis than the same components from normal animals or animals fed low-energy diets. The "double-muscling" characteristic had a greater effect on rate of in vitro protein synthesis than did high or low-energy diets. Cytoplasmic enzymes and polysomes from calves supported a greater rate of in vitro protein synthesis than the same components from 18- to 24-mo-old animals or cows. Based on these limited results in one species and with two groups of animals in that species, cytoplasmic enzymes may have a greater role in limiting rate of muscle protein synthesis in the current population of domestic animals than polysomes. Composition of the crude cytoplasmic enzyme fraction used in this study is unknown, but it likely contains elongation and termination factors in addition to aminoacyl-tRNA synthases and regulatory RNA.
mesh_terms: D000367:Age Factors; D000821:Animal Feed; D000818:Animals; D002250:Carbon Radioisotopes; D002417:Cattle / Q000235:genetics / Q000378:metabolism*; D002474:Cell-Free System; D003593:Cytoplasm / Q000201:enzymology*; D005260:Female; D007930:Leucine / Q000378:metabolism; D008297:Male; D024510:Muscle Development; D009124:Muscle Proteins / Q000096:biosynthesis*; D009132:Muscles / Q000378:metabolism*; D011132:Polyribosomes / Q000378:metabolism*; D013347:Subcellular Fractions / Q000378:metabolism
chemical_list: D002250:Carbon Radioisotopes; D009124:Muscle Proteins; D007930:Leucine