Muscle protein degradation and amino acid metabolism during prolonged knee-extensor exercise in humans

1999 ◽  
Vol 97 (5) ◽  
pp. 557 ◽  
Author(s):  
G. VAN HALL ◽  
B. SALTIN ◽  
A.J.M. WAGENMAKERS
Keyword(s):  
Amino Acid ◽  
Protein Degradation ◽  
Amino Acid Metabolism ◽  
Acid Metabolism ◽  
Muscle Protein ◽  
Knee Extensor ◽  
Muscle Protein Degradation ◽  
Exercise In Humans

scholarly journals Rates of protein synthesis in skin and bone, and their importance in the assessment of protein degradation in the perfused rat hemicorpus

1981 ◽  
Vol 194 (1) ◽  
pp. 373-376 ◽  
Author(s):  
V R Preedy ◽  
P J Garlick
Keyword(s):  
Protein Synthesis ◽  
Amino Acid ◽  
Protein Degradation ◽  
Muscle Tissue ◽  
Amino Acid Metabolism ◽  
Acid Metabolism ◽  
Muscle Protein ◽  
Muscle Metabolism ◽  
Muscle Protein Degradation

The perfused rat hemicorpus preparation, which has frequently been used to study muscle metabolism, contains 39% by weight of non-muscle tissue such as skin and bone. Both the concentration of RNA and the incorporation of [U-14C]tyrosine into protein indicate that the non-muscle components are more active in protein synthesis than is muscle. These observations have important implications for studies of amino acid metabolism, and in particular for the measurement of muscle protein degradation in the hemicorpus.

Muscle protein degradation and amino acid metabolism during prolonged knee-extensor exercise in humans

1999 ◽  
Vol 97 (5) ◽  
pp. 557-567 ◽  
Author(s):  
G. VAN HALL ◽  
B. SALTIN ◽  
A. J. M. WAGENMAKERS
Keyword(s):  
Amino Acids ◽  
Amino Acid ◽  
Protein Degradation ◽  
Acid Production ◽  
Glycogen Content ◽  
Muscle Protein ◽  
Knee Extensor ◽  
Total Amino Acid ◽  
Amino Acid Production ◽  
Muscle Protein Degradation

The aim of this study was to investigate whether prolonged one-leg knee-extensor exercise enhances net protein degradation in muscle with a normal or low glycogen content. Net amino acid production, as a measure of net protein degradation, was estimated from leg exchange and from changes in the concentrations of amino acids that are not metabolized in skeletal muscle. Experiments were performed at rest and during one-leg knee-extensor exercise in six subjects having one leg with a normal glycogen content and the other with a low glycogen content. Exercise was performed for 90 min at a workload of 60–65% of maximal one-leg power output, starting either with the normal-glycogen or the low-glycogen leg, at random. The net production of threonine, lysine and tyrosine and the sum of the non-metabolized amino acids were 9–20-fold higher (P< 0.05) during exercise of the normal-glycogen leg than at rest. Total amino acid production was also 10-fold higher during exercise compared with that at rest (difference not significant). The net production rates of threonine, glycine and tyrosine and of the sum of the non-metabolized amino acids were about 1.5–2.5-fold higher during exercise with the leg with a low glycogen content compared with the leg with a normal glycogen content (P< 0.05). Total amino acid production was 1.5-fold higher during exercise for the low-glycogen leg compared with the normal-glycogen leg (difference not significant). These data indicate that prolonged one-leg knee-extensor exercise leads to a substantial increase in net muscle protein degradation, and that a lowering of the starting muscle glycogen content leads to a further increase. The carbon atoms of the branched-chain amino acids (BCAA), glutamate, aspartate and asparagine, liberated by protein degradation, and the BCAA and glutamate extracted in increased amounts from the blood during exercise, are used for the synthesis of glutamine and for tricarboxylic-acid cycle anaplerosis.

scholarly journals Reducing plasma HIV RNA improves muscle amino acid metabolism

2005 ◽  
Vol 288 (1) ◽  
pp. E278-E284 ◽  
Author(s):  
Kevin E. Yarasheski ◽  
Samuel R. Smith ◽  
William G. Powderly
Keyword(s):  
Protein Synthesis ◽  
Amino Acid ◽  
Amino Acid Metabolism ◽  
Acid Metabolism ◽  
Muscle Protein ◽  
Muscle Protein Synthesis ◽  
Synthesis Rate ◽  
Protein Synthesis Rate ◽  
Hiv Rna ◽  
Muscle Protein Synthesis Rate

We reported (Yarasheski KE, Zachwieja JJ, Gischler J, Crowley J, Horgan MM, and Powderly WG. Am J Physiol Endocrinol Metab 275: E577–E583, 1998) that AIDS muscle wasting was associated with an inappropriately low rate of muscle protein synthesis and an elevated glutamine rate of appearance (Ra Gln). We hypothesized that high plasma HIV RNA caused dysregulation of muscle amino acid metabolism. We determined whether a reduction in HIV RNA (≥1 log) increased muscle protein synthesis rate and reduced Ra Gln and muscle proteasome activity in 10 men and 1 woman (22–57 yr, 60–108 kg, 17–33 kg muscle) with advanced HIV (CD4 = 0–311 cells/μl; HIV RNA = 10–375 × 103 copies/ml). We utilized stable isotope tracer methodologies ([13C]Leu and [15N]Gln) to measure the fractional rate of mixed muscle protein synthesis and plasma Ra Gln in these subjects before and 4 mo after initiating their first or a salvage antiretroviral therapy regimen. After treatment, median CD4 increased (98 vs. 139 cells/μl, P = 0.009) and median HIV RNA was reduced (155,828 vs. 100 copies/ml, P = 0.003). Mixed muscle protein synthesis rate increased (0.062 ± 0.005 vs. 0.078 ± 0.006%/h, P = 0.01), Ra Gln decreased (387 ± 33 vs. 323 ± 15 μmol·kg fat-free mass−1·h−1, P = 0.04), and muscle proteasome chymotrypsin-like catalytic activity was reduced 14% ( P = 0.03). Muscle mass was only modestly increased (1 kg, P = not significant). We estimated that, for each 10,000 copies/ml reduction in HIV RNA, ∼3 g of additional muscle protein are synthesized per day. These findings suggest that reducing HIV RNA increases muscle protein synthesis and reduces muscle proteolysis, but muscle protein synthesis relative to whole body protein synthesis rate is not restored to normal, so muscle mass is not substantially increased.

Amino acid metabolism after intense exercise

1990 ◽  
Vol 258 (2) ◽  
pp. E249-E255 ◽  
Author(s):  
J. T. Devlin ◽  
I. Brodsky ◽  
A. Scrimgeour ◽  
S. Fuller ◽  
D. M. Bier
Keyword(s):  
Protein Synthesis ◽  
Amino Acid ◽  
Protein Degradation ◽  
Amino Acid Metabolism ◽  
Acid Metabolism ◽  
Recovery Period ◽  
Whole Body ◽  
Protein Breakdown ◽  
Body Protein ◽  
Leucine Oxidation

We studied postexercise amino acid metabolism, in the whole body and across the forearm. Seven volunteers were infused with L-[alpha-15N]lysine and L-[1-13C]-leucine twice [one time during 3 h after cycle exercise (75% VO2max), and one time in the resting state]. Whole body protein breakdown was estimated from dilution of L-[alpha-15N]lysine and L-[1-13C]ketoisocaproic acid (KIC) enrichments in plasma. Leucine oxidation was calculated from 13CO2 enrichments in expired air. Whole body protein breakdown was not increased above resting levels during the recovery period. Leucine oxidation was decreased after exercise (postexercise 13 +/- 2.3 vs. resting 19 +/- 3.2 mumol.kg-1.h-1; P less than 0.02), while nonoxidative leucine disposal was increased (115 +/- 6.1 vs. 103 +/- 5.6 micrograms.kg-1.min-1; P less than 0.02). After exercise, forearm net lysine balance was unchanged (87 +/- 25 vs. 93 +/- 28 nmol.100 ml-1.min-1), but there were decreases in forearm muscle protein degradation (219 +/- 51 vs. 356 +/- 85 nmol.100 ml-1.min-1; P less than 0.05) and synthesis (132 +/- 41 vs. 255 +/- 69 nmol.100 ml-1.min-1; P less than 0.01). In conclusion, after exercise 1) whole body protein degradation is not increased, 2) leucine disposal is directed away from oxidative and toward nonoxidative pathways, 3) forearm protein synthesis is decreased. Postexercise increases in whole body protein synthesis occur in tissues other than nonexercised muscle.

scholarly journals Protein degradation and amino acid metabolism by propionibacteria

1995 ◽  
Vol 75 (4-5) ◽  
pp. 325-330 ◽  
Author(s):  
T. Langsrud ◽  
T. Sorhaug ◽  
G. E. Vegarud
Keyword(s):  
Amino Acid ◽  
Protein Degradation ◽  
Amino Acid Metabolism ◽  
Acid Metabolism
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