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Iowa State University,7, Ames 50011
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.
1 Journal Paper No. J-11174 of the Iowa Agr. and Home Econ. Exp. Sta., Ames, Projects 2361 and 2127. This research was supported in part by Arizona Agr. Exp. Sta., Project 28, and by grants from the National Institutes of Health to DEG (AM-19864 and HL-20984) and to RMR (HL-15679), from the Muscular Dystrophy Assoc. (DEG and RMR), and the American Heart Assoc., Iowa Affiliate (RMR). This paper is a contribution from North Central Reg. Res. Proj. NC131.
2 We gratefully acknowledge the technical assistance of Jacqueline Harvey Martin and Darlene Markley, and the help of Donna Mencinger and Joan Andersen with the manuscript. The "double-muscled" and "normal" animals used in the experiments described in this manuscript were obtained from the Texas A&M Univ. herd, and we deeply appreciate the assistance of O. D. Butler and his faculty in making these animals available to us.
3 Present address is: Baylor College of Medicine, Dept. of Med., Houston, TX 77030.
4 Send reprint requests and other queries to Darrel E. Goll, Muscle Biology Group, Univ. of Arizona, Tucson 85721.
5 Muscle Biology Group, Iowa State Univ., Ames 50011.
6 Dept. of Food Sci. and Human Nutr., Michigan State Univ., East Lansing 48824.
7 Departments of Anim. Sci., Biochem. and Biophys., and Food Technol., Cooperating.
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