Branched chain amino acids as a major source of alanine nitrogen in man

M. W. Haymond, J. M. Miles

Research output: Contribution to journalArticle

60 Citations (Scopus)

Abstract

In vitro perfusion and incubation studies and recent investigations in dogs suggest that branched chain amino acids (BCAA)may be a major source of alanine nitrogen. To determine the contribution of BCAA nitrogen to the formation of alanine in man, seven postabsorptive adults received prime-dose constant infusions of 15N-leucine, L-[6,6,6-2H3] leucine, and L-[2,3,3,3-2H4] alanine; isotopic enrichment was determined in arterialized venous plasma samples by gas chromatography-mass spectroscopy. At substrate and isotope steady state, alanine flux and the rate of 15N alanine appearance were 5.4 ± 0.3 μmol/kg.min and 32 ± 2 nmol/kg.min, respectively. Leucine nitrogen flux was significantly greater than that of leucine carbon flux (2.54 ± 0.25 vs. 1.90 ± 0.10 μmol/kg.min, respectively; P < 0.001). Greater flux of leucine nitrogen when compared with leucine carbon suggests significant recycling of the leucine carbon in vivo. The percent of circulating alanine nitrogen derived from leucine was 12.5 ± 1.5%; however, the rate of leucine nitrogen transferred to alanine was 0.66 ± 0.05 μmol/kg.min, and represents a minimum of 28% of leucine nitrogen going to alanine. On the basis of these data, together with the percent of alanine and leucine in body protein, only 40% of circulating plasma alanine could come from endogenous protein, whereas 60% is derived from de novo synthesis. In addition, at least 20% of the nitrogen required for alanine synthesis is derived solely from leucine following an overnight fast. Therefore, if the contribution of isoleucine and valine nitrogen is similar to that of leucine, the BCAA may contribute to a minimum of 60% of the nitrogen required for alanine synthesis in postabsorptive man.

Original languageEnglish (US)
Pages (from-to)86-89
Number of pages4
JournalDiabetes
Volume31
Issue number1
StatePublished - 1982

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Branched Chain Amino Acids
Leucine
Alanine
Nitrogen
Carbon
Plasma Gases
Carbon Cycle
Isoleucine
Valine
Recycling
Isotopes
Gas Chromatography
Mass Spectrometry

ASJC Scopus subject areas

  • Endocrinology, Diabetes and Metabolism
  • Internal Medicine

Cite this

Haymond, M. W., & Miles, J. M. (1982). Branched chain amino acids as a major source of alanine nitrogen in man. Diabetes, 31(1), 86-89.

Branched chain amino acids as a major source of alanine nitrogen in man. / Haymond, M. W.; Miles, J. M.

In: Diabetes, Vol. 31, No. 1, 1982, p. 86-89.

Research output: Contribution to journalArticle

Haymond, MW & Miles, JM 1982, 'Branched chain amino acids as a major source of alanine nitrogen in man', Diabetes, vol. 31, no. 1, pp. 86-89.
Haymond, M. W. ; Miles, J. M. / Branched chain amino acids as a major source of alanine nitrogen in man. In: Diabetes. 1982 ; Vol. 31, No. 1. pp. 86-89.
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abstract = "In vitro perfusion and incubation studies and recent investigations in dogs suggest that branched chain amino acids (BCAA)may be a major source of alanine nitrogen. To determine the contribution of BCAA nitrogen to the formation of alanine in man, seven postabsorptive adults received prime-dose constant infusions of 15N-leucine, L-[6,6,6-2H3] leucine, and L-[2,3,3,3-2H4] alanine; isotopic enrichment was determined in arterialized venous plasma samples by gas chromatography-mass spectroscopy. At substrate and isotope steady state, alanine flux and the rate of 15N alanine appearance were 5.4 ± 0.3 μmol/kg.min and 32 ± 2 nmol/kg.min, respectively. Leucine nitrogen flux was significantly greater than that of leucine carbon flux (2.54 ± 0.25 vs. 1.90 ± 0.10 μmol/kg.min, respectively; P < 0.001). Greater flux of leucine nitrogen when compared with leucine carbon suggests significant recycling of the leucine carbon in vivo. The percent of circulating alanine nitrogen derived from leucine was 12.5 ± 1.5{\%}; however, the rate of leucine nitrogen transferred to alanine was 0.66 ± 0.05 μmol/kg.min, and represents a minimum of 28{\%} of leucine nitrogen going to alanine. On the basis of these data, together with the percent of alanine and leucine in body protein, only 40{\%} of circulating plasma alanine could come from endogenous protein, whereas 60{\%} is derived from de novo synthesis. In addition, at least 20{\%} of the nitrogen required for alanine synthesis is derived solely from leucine following an overnight fast. Therefore, if the contribution of isoleucine and valine nitrogen is similar to that of leucine, the BCAA may contribute to a minimum of 60{\%} of the nitrogen required for alanine synthesis in postabsorptive man.",
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