HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text Full Text (PDF) Purchase Article View Shopping Cart Alert me when this article is cited Alert me if a correction is posted Citation Map Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Raguso, C. A Articles by Young, V. R Search for Related Content PubMed PubMed Citation Articles by Raguso, C. A Articles by Young, V. R Agricola Articles by Raguso, C. A Articles by Young, V. R

A tracer investigation of obligatory oxidative amino acid losses in healthy, young adults^1,2,3

¹ From the Laboratory of Human Nutrition, School of Science and Clinical Research Center, Massachusetts Institute of Technology, Cambridge.

Background: Estimation of the minimum requirement for indispensable amino acids (IAAs) has been attempted by assuming that obligatory oxidative losses (OOLs) of IAAs can be approximated from nitrogen losses and that the efficiency of utilization of IAAs at requirement intakes is 70%.

Objective: We wished to determine the rates of OOLs in healthy adults, using L-[1-¹³C]leucine and L-[1-¹³C, methyl-²H₃]methio-nine as tracers, after adjustment to a protein-free diet and how these rates compare with those when either sulfur amino acids (SAAs: methionine and cyst(e)ine) or leucine were removed from an otherwise adequate diet.

Design: Eleven subjects were randomly assigned to a 5-d protein-free diet or a 5-d diet providing adequate nitrogen and amino acids except for the SAAs or leucine. A 24-h constant intravenous infusion of [¹⁵N,¹⁵N]urea and L-[1-¹³C]leucine (Leu group; n = 5) or L-[1-¹³C, methyl-²H₃]methionine (Met group; n = 6 ) began at 1800 on day 5 and rates of amino acid oxidation were determined.

Results: Mean (±SD) oxidation rates (mg•kg^-1•d^-1) of methionine and leucine were 6.4 ± 1.4 and 24.7 ± 3.6, respectively, with the protein-free diet; rates were significantly lower (3.9 ± 2.2 and 7.2 ± 3.4, respectively) after the SAA- and leucine-free diets. Urea production was significantly lower (P < 0.01) with the protein-free than with the SAA- or leucine-free diet.

Conclusions: Isotopically determined OOLs for methionine and leucine are consistent with losses predicted from nitrogen excretion, and consistent with our previous measurements of cysteine oxidation as an index of total SAA losses. The data further support our earlier conclusions regarding methionine sparing by cysteine and tentative recommended SAA requirements in adults.

Key Words: Methionine metabolism • leucine metabolism • obligatory oxidative losses • indispensable amino acid minimum requirement • sulfur amino acids • cyst(e)ine • leucine • humans

This article has been cited by other articles:

				N. K. Fukagawa Sparing of Methionine Requirements: Evaluation of Human Data Takes Sulfur Amino Acids Beyond Protein J. Nutr., June 1, 2006; 136(6): 1676S - 1681S. [Abstract] [Full Text] [PDF]

				M. Di Buono, L. J. Wykes, D. E. C. Cole, R. O. Ball, and P. B. Pencharz Regulation of Sulfur Amino Acid Metabolism in Men in Response to Changes in Sulfur Amino Acid Intakes J. Nutr., March 1, 2003; 133(3): 733 - 739. [Abstract] [Full Text] [PDF]

				A. V Kurpad, T. Raj, A. El-Khoury, R. Kuriyan, K. Maruthy, S. Borgonha, D. Chandukudlu, M. M Regan, and V. R Young Daily requirement for and splanchnic uptake of leucine in healthy adult Indians Am. J. Clinical Nutrition, December 1, 2001; 74(6): 747 - 755. [Abstract] [Full Text]

				M. Di Buono, L. J Wykes, R. O Ball, and P. B Pencharz Total sulfur amino acid requirement in young men as determined by indicator amino acid oxidation with L-[1- Am. J. Clinical Nutrition, December 1, 2001; 74(6): 756 - 760. [Abstract] [Full Text]

				M. Di Buono, L. J Wykes, R. O Ball, and P. B Pencharz Dietary cysteine reduces the methionine requirement in men Am. J. Clinical Nutrition, December 1, 2001; 74(6): 761 - 766. [Abstract] [Full Text]

				M. J. MacCoss, N. K. Fukagawa, and D. E. Matthews Measurement of intracellular sulfur amino acid metabolism in humans Am J Physiol Endocrinol Metab, June 1, 2001; 280(6): E947 - E955. [Abstract] [Full Text] [PDF]

				J. F Gregory III, G. J Cuskelly, B. Shane, J. P Toth, T. G Baumgartner, and P. W Stacpoole Primed, constant infusion with [2H3]serine allows in vivo kinetic measurement of serine turnover, homocysteine remethylation, and transsulfuration processes in human one-carbon metabolism Am. J. Clinical Nutrition, December 1, 2000; 72(6): 1535 - 1541. [Abstract] [Full Text] [PDF]

				P. J. Reeds Dispensable and Indispensable Amino Acids for Humans J. Nutr., July 1, 2000; 130(7): 1835S - 1840. [Abstract] [Full Text]

				V. R. Young and S. Borgonha Nitrogen and Amino Acid Requirements: : The Massachusetts Institute of Technology Amino Acid Requirement Pattern J. Nutr., July 1, 2000; 130(7): 1841S - 1849. [Abstract] [Full Text]

				J. Lyons, A. Rauh-Pfeiffer, Y. M. Yu, X.-M. Lu, D. Zurakowski, R. G. Tompkins, A. M. Ajami, V. R. Young, and L. Castillo Blood glutathione synthesis rates in healthy adults receiving a sulfur amino acid-free diet PNAS, May 9, 2000; 97(10): 5071 - 5076. [Abstract] [Full Text] [PDF]