Branched-chain amino acid metabolism in skeletal muscte promotes the production of alanine, an important precursor in hepatic gluconeogenesis. There is controversy concerning the origin of the carbon skeleton of alanine produced in muscle, specifically whether it is derived from carbohydrate via glycolysis (the glucose-alanine cycle) or from amino acid precursors (viz. glutamate, valine, isoleucine, methionine, aspartate, asparagine) via a pathway involving phosphoenolpyruvate (PEP) carboxykinase and pyruvate kinase, or NADP-malate dehydrogenase (malic enzyme). The relevant literature is reviewed and it is concluded that neogenic flux from amino acids is unlikely to be of major quantitative importance for provision of the carbon skeleton of alanine either in vitro or in vivo. Evidence is presented that branched-chain amino acid oxidation in muscle is incomplete and that the branched-chain 2-oxo acids and the products of their partial oxidation (including glutamine) are released. The role of these metabolites is discussed in the context of fuel homeostasis in starvation.
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Review Article|
December 01 1985
Alanine and inter-organ relationships in branched-chain amino and 2-oxo acid metabolism: Review
T. Norman Palmer;
T. Norman Palmer
1Department of Biochemistry, Charing Cross and Westminster Medical School, Fulham Palace Road, London W6 8RF, UK
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Margaret A. Caldecourt;
Margaret A. Caldecourt
1Department of Biochemistry, Charing Cross and Westminster Medical School, Fulham Palace Road, London W6 8RF, UK
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Keith Snell;
Keith Snell
2Department of Biochemistry, University of Surrey, Guildford, Surrey GU2 5XH, UK
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Mary C. Sugden
Mary C. Sugden
3Department of Chemical Pathology, London Hospital Medical College, Turner Street, London E1 2AD, UK
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Publisher: Portland Press Ltd
Received:
November 12 1985
Online ISSN: 1573-4935
Print ISSN: 0144-8463
© 1985 The Biochemical Society
1985
Biosci Rep (1985) 5 (12): 1015–1033.
Article history
Received:
November 12 1985
Citation
T. Norman Palmer, Margaret A. Caldecourt, Keith Snell, Mary C. Sugden; Alanine and inter-organ relationships in branched-chain amino and 2-oxo acid metabolism: Review. Biosci Rep 1 December 1985; 5 (12): 1015–1033. doi: https://doi.org/10.1007/BF01119623
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