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ALT1-encoded alanine aminotransferase plays a central role in the metabolism of alanine in Saccharomyces cerevisiae

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In the yeast Saccharomyces cerevisiae, the paralogous genes ALT1 and ALT2 have been proposed to encode alanine aminotransferase isozymes. Although in other microorganisms this enzyme constitutes the main pathway for alanine biosynthesis, its role in S. cerevisiae had remained unclear. Results presented in this paper show that under respiratory conditions, Alt1p constitutes the sole pathway for alanine biosynthesis and catabolism, constituting the first example of an alanine aminotransferase that simultaneously carries out both functions. Conversely, under fermentative conditions, it plays a catabolic role and alanine is mainly synthesized through an alternative pathway. It can thus be concluded that ALT1 has functions in alanine biosynthesis and utilization or only alanine utilization under respiratory and fermentative conditions, respectively. ALT2 expression was repressed under all tested conditions, suggesting that Alt2p biosynthesis is strictly controlled and only allowed to express under peculiar physiological conditions.

Chez la levure Saccharomyces cerevisiae, les gènes paralogues ALT1 et ALT2 codent vraisemblablement des isozymes de l’alanine aminotransférase. Quoique cette enzyme constitue la voie principale de biosynthèse de l’alanine chez d’autres microorganismes, son rôle chez S. cerevisiae demeure obscur. Les résultats présentés dans cet article démontrent que lors de la respiration, Alt1p constitue la seule voie de biosynthèse et de catabolisme de l’alanine, constituant le premier exemple d’une alanine aminotransférase qui possède simultanément les deux fonctions. À l’inverse, lors de la fermentation, elle joue un rôle catabolique et l’alanine est synthétisée par une voie alternative. On peut donc conclure que ALT1 possède des fonctions dans la biosynthèse et l’utilisation de l’alanine, ou dans l’utilisation de l’alanine seulement, lors de la respiration et la fermentation respectivement. L’expression de ALT2 était réprimée dans toutes les conditions étudiées, ce qui suggère que la biosynthèse de Alt2p est strictement contrôlée et que l’enzyme ne s’exprime que sous des conditions physiologiques particulières.

Document Type: Research Article

Publication date: 2009-04-01

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  • Published since 1954, this monthly journal contains new research in the field of microbiology including applied microbiology and biotechnology; microbial structure and function; fungi and other eucaryotic protists; infection and immunity; microbial ecology; physiology, metabolism and enzymology; and virology, genetics, and molecular biology. It also publishes review articles and notes on an occasional basis, contributed by recognized scientists worldwide.
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