title: Effect of rate of catabolism of DL-[1-14C]lysine on estimation of whole body protein synthesis in rats.
abstract: We investigated the effect of rate of DL-[1-14C]lysine metabolism on the estimation of whole body protein synthesis in rats. Growing rats were given single injections of DL-[1-14C]lysine via a tail vein and cumulative expiration of 14CO2 was measured after 3, 6 and 9 hours. Total 14C in protein-bound lysine, body lipids, perchloric acid-soluble material, urine, feces and gastrointestinal contents was recovered after 9 hours. After correcting for radiochemical purity and stereoisomerism of DL-[1-14C]lysine, 95.1% of injected L-[1-14C]lysine was found in expired air and protein-bound [14C]lysine. Daily nitrogen retention of rats was 150 mg and daily incorporation of lysine into body protein was 119% of that absorbed from the gastrointestinal tract, from which rates of whole body protein synthesis, accretion and degradation were estimated to be 2.58, 0.76 and 1.83 g/day, respectively. Expressed per unit of body weight the rate of protein synthesis was not significantly different from previous estimates using L-[1-14C]leucine, which indicated that differences in catabolic pathways of leucine and lysine as well as differences in intracellular specific activities of these [14C]amino acids had a negligible effect on the estimation of protein synthesis.
mesh_terms: D000818:Animals; D002245:Carbon Dioxide; D007408:Intestinal Absorption; D007700:Kinetics; D050356:Lipid Metabolism; D008239:Lysine / Q000378:metabolism*; D008297:Male; D009584:Nitrogen / Q000378:metabolism; D010472:Perchlorates; D014176:Protein Biosynthesis; D051381:Rats; D012995:Solubility; D013237:Stereoisomerism
chemical_list: D010472:Perchlorates; D002245:Carbon Dioxide; D008239:Lysine; D009584:Nitrogen