TY - JOUR
T1 - The roles of galactitol, galactose-1-phosphate, and phosphoglucomutase in galactose-induced toxicity in Saccharomyces cerevisiae
AU - de Jongh, Willem A
AU - Bro, Christoffer
AU - Ostergaard, Simon
AU - Regenberg, Birgitte
AU - Olsson, Lisbeth
N1 - Keywords: Culture Media; Galactitol; Galactokinase; Galactose; Galactosephosphates; Multienzyme Complexes; Phosphoglucomutase; Plasmids; Saccharomyces cerevisiae; Saccharomyces cerevisiae Proteins; Trans-Activators
PY - 2008
Y1 - 2008
N2 - The uptake and catabolism of galactose by the yeast Saccharomyces cerevisiae is much lower than for glucose and fructose, and in applications of this yeast for utilization of complex substrates that contain galactose, for example, lignocellulose and raffinose, this causes prolonged fermentations. Galactose is metabolized via the Leloir pathway, and besides the industrial interest in improving the flux through this pathway it is also of medical relevance to study the Leloir pathway. Thus, genetic disorders in the genes encoding galactose-1-phosphate uridylyltransferase or galactokinase result in galactose toxicity both in patients with galactosemia and in yeast. In order to elucidate galactose related toxicity, which may explain the low uptake and catabolic rates of S. cerevisiae, we have studied the physiological characteristics and intracellular metabolite profiles of recombinant S. cerevisiae strains with improved or impaired growth on galactose. Aerobic batch cultivations on galactose of strains with different combinations of overexpression of the genes GAL1, GAL2, GAL7, and GAL10, which encode proteins that together convert extracellular galactose into glucose-1-phosphate, revealed a decrease in the maximum specific growth rate when compared to the reference strain. The hypothesized toxic intermediate galactose-1-phosphate cannot be the sole cause of galactose related toxicity, but indications were found that galactose-1-phosphate might cause a negative effect through inhibition of phosphoglucomutase. Furthermore, we show that galactitol is formed in S. cerevisiae, and that the combination of elevated intracellular galactitol concentration, and the ratio between galactose-1-phosphate concentration and phosphoglucomutase activity seems to be important for galactose related toxicity causing decreased growth rates.
AB - The uptake and catabolism of galactose by the yeast Saccharomyces cerevisiae is much lower than for glucose and fructose, and in applications of this yeast for utilization of complex substrates that contain galactose, for example, lignocellulose and raffinose, this causes prolonged fermentations. Galactose is metabolized via the Leloir pathway, and besides the industrial interest in improving the flux through this pathway it is also of medical relevance to study the Leloir pathway. Thus, genetic disorders in the genes encoding galactose-1-phosphate uridylyltransferase or galactokinase result in galactose toxicity both in patients with galactosemia and in yeast. In order to elucidate galactose related toxicity, which may explain the low uptake and catabolic rates of S. cerevisiae, we have studied the physiological characteristics and intracellular metabolite profiles of recombinant S. cerevisiae strains with improved or impaired growth on galactose. Aerobic batch cultivations on galactose of strains with different combinations of overexpression of the genes GAL1, GAL2, GAL7, and GAL10, which encode proteins that together convert extracellular galactose into glucose-1-phosphate, revealed a decrease in the maximum specific growth rate when compared to the reference strain. The hypothesized toxic intermediate galactose-1-phosphate cannot be the sole cause of galactose related toxicity, but indications were found that galactose-1-phosphate might cause a negative effect through inhibition of phosphoglucomutase. Furthermore, we show that galactitol is formed in S. cerevisiae, and that the combination of elevated intracellular galactitol concentration, and the ratio between galactose-1-phosphate concentration and phosphoglucomutase activity seems to be important for galactose related toxicity causing decreased growth rates.
U2 - 10.1002/bit.21890
DO - 10.1002/bit.21890
M3 - Journal article
C2 - 18421797
SN - 0006-3592
VL - 101
SP - 317
EP - 326
JO - Biotechnology and Bioengineering
JF - Biotechnology and Bioengineering
IS - 2
ER -