FEMS Microbiology Letters 42 (1987) 213-220 213 Published by Elsevier FEM 02809 Anabolic role of L-malic acid in Saccharomyces cerevisiae in anaerobiosis during alcoholic fermentation J.M. Salmon, F. Vezinhet and P. Barre Laboratoire de Microbiologie et de Technologie des Fermentations, Institut des Produits de la Vigne, INRA, place Viala, 34060 Montpellier C~dex, France Received 12 December1986 Accepted 28 February 1987 Key words: Saccharomyces cereoisme; L-Malic acid; Anaerobiosis; Ethanol 1. SUMMARY In anaerobiosis, pyruvate carboxylase activity can be greatly reduced by limiting the availability of biotin to yeast cells. In these conditions an incorporation of carbon from exogenous L-malic acid can be observed. The main pathway used for this anabolic utilization goes through malate dehy- drogenase and the oxidative reactions of the tri- carboxylic acid cycle. This anabolic function of E-malic acid is strongly inhibited by a residual glucose concentration in the fermenter. This in- hibition may be due, in this condition, to a higher intracellular concentration of some negative effec- tots of malate dehydrogenase such as: 1,6-fructose diphosphate, glyceraldehyde 3-phosphate, ATP and ADP. 2. INTRODUCTION During anaerobiosis, C6-skeleton sugars such as glucose are catabolized via the glycolysis pathway Correspondence to: J.M. Salmon, Laboratoire de Microbiologie et de Technologiedes Fermentations, Institut des Produits de la Vigne, INRA, place Viala, F-34060 Montpellier C6dex, France. to pyruvate, which is decarboxylated to acetalde- hyde which acts as the terminal electron acceptor. Ethanol is then the major end-product. This path- way is mainly orientated to cell energy produc- tion. A weak part of the intracellular pyruvate pool is used to prepare building blocks for the biosynthetic pathways via the subsisting two branches of the tricarboxylate pathway in anaerobiosis [1]. An oxidative branch leads to a-ketoglutarate, serving a purely biosynthetic role, while a reductive branch leads to succinate and serves either a biosynthetic or an amphibolic role: the a-ketoglutarate dehydrogenase step between these branches is repressed during anaerobiosis [2-4]. In these conditions, C4-skeleton compounds are synthetized via pyruvate carboxylase (E.C.6.4.1.1), the glyoxylic acid shunt being impaired under anaerobiosis and glucose repression [5-7]. - After previous results obtained in our labora- tory [8], we postulated that when the pyruvate carboxylase activity is greatly reduced, the degradation of exogenous C4-skeleton compounds such as L-malic acid could play an anabolic role and we tried to elucidate the metabolic pathways involved. 0378-1097/87/$03.50 © 1987 Federation of European MicrobiologicalSocieties Downloaded from https://academic.oup.com/femsle/article-abstract/42/2-3/213/517329 by guest on 21 May 2020