Biotin and the Metabolism of Baker's Yeast

Abstract

Based on experimental results and the results presented in the literature a model for the meta bolism of baker's yeast under biotin deficiency is presented. In these conditions the most sensi tive point in the metabolism is the carboxylation of pyruvate to oxaloacetate catalyzed by the biotin-containing pyruvate carboxylase. Because the rate of glycolysis is not affected by biotindeficiency pyruvate accumulates in the cells and is partially excreted into the medium. The high pyruvate pool in the cells means that the metabolism is mainly fermentative even in vigorously aerated cultures. The oxidation of pyruvate to acetyl-CoA proceeds almost unaffected, as can be seen by the production of elevated amounts of ethyl acetate by yeast grown under sub-optimal biotin concentrations. Acetyl-CoA carboxylase, which also has biotin as the prosthetic group, is not as sensitive to a deficiency of this growth factor as is pyruvate carboxylase. In yeast grown without biotin the amounts of fatty acids and lipids are the same or even higher than in cells grown under optimal conditions. The metabolism from oxaloacetate towards the TCA cycle and glutamate is not affected as strongly as is the metabolism to aspartate, which is present in cells in strictly limited amounts. This causes an over-production of metabolic intermediates, e.g. diazotizable arylamine and hypoxanthine as well as citrulline. Their conversion to normal cell constituents, purine nucleotides and arginine, is dependent on the aspartate available and is thus depressed by lack of biotin.

The influence of nitrogen and biotin interactions on the performance of Saccharomyces in alcoholic fermentations

“…Davenport (1985) noted that concentrations of 0·7 to 1·3 μ g l −1 were sufficient for commercial active dry wine yeast strains to complete fermentations of synthetic grape juice media. However, these fermentations also contained very high concentrations of YAN (400 mg l −1 ) that may have altered the minimum concentrations of biotin required by the yeasts (Moat and Emmons 1954; Ahmad and Rose 1962b; Oura and Suomalainen 1978). Maximum growth and fermentation rates under varying YAN and biotin concentrations have been reported (Ough et al.…”

“…1989; Henschke and Jiranek 1993). While the nitrogen content of a medium is an important global regulator of yeast gene expression and metabolism (Cooper 1982; Jones and Fink 1982), the role of biotin in nitrogen and lipid metabolism has been established (Oura and Suomalainen 1978; Lynen 1979; Keech and Wallace 1985).…”

“…A lack of biotin may also be of concern (Monk and Costello 1984; Boulton et al. 1996) as Saccharomyces cerevisiae strains used in industrial fermentations are auxotrophic for biotin (Kunkee and Amerine 1970; Oura and Suomalainen 1978,1982; Monk 1994), and the vitamin is involved in nitrogen metabolism by the yeast (Oura and Suomalainen 1978). Biotin is required by the enzyme urea carboxylase, which is necessary for the utilization of nitrogen from arginine (Cooper 1982), a key amino acid in grape must (Spayd and Andersen‐Bagge 1996) and storage form of nitrogen for yeast (Whitney et al.…”

COMPARISON OF HEADSPACE SOLID PHASE MICROEXTRACTION AND XAD‐2 METHODS TO EXTRACT VOLATILE COMPOUNDS PRODUCED BY SACCHAROMYCES DURING WINE FERMENTATIONS

“…Volatile compounds produced by Saccharomyces during wine fermentation affect the sensory qualities of wine (Oura and Suomalainen 1978; Bertrand 1983; Etievant 1991; Guth 1997a, b; Fleet 2003). The ability to accurately extract and analyze these compounds can help winemakers formulate decisions to facilitate the production of wines with specific yeast‐derived flavors and aromas (Berry and Watson 1987; Pretorius 2000; Reynolds et al.…”

Viscoadaptation controls intracellular reaction rates in response to heat and energy availability

“…However, when cells were grown in low biotin media, as required for the biotinylation assays, 0% glucose induced viscoadaptation (Supp Fig 10). In low biotin conditions cells poorly metabolize glucose, which results in a constitutive intracellular glucose pool ( 32 ) . We therefore speculate that this residual glucose enables cells in low biotin to initiate viscoadaptation despite 0% glucose.…”