Regulation of glycolytic enzymes and the Crabtree effect in galactose-limited continuous cultures of Saccharomyces cerevisiae.
In order to determine whether the changes in the activities and mRNA levels of enzymes involved in intermediary carbon metabolism previously observed in glucose-limited continuous cultures (Sierkstra et al., 1992a) were glucose specific, we have analysed their regulation in a galactose-limited continuous culture of Saccharomyces cerevisiae. The Vmax of the galactose uptake system was shown to be dilution rate (D) dependent, comparable with the high-affinity glucose uptake. The maximum uptake was observed at D 0.2 h-1 (0.25 mmol min-1 per g) and the minimum uptake (0.1 mmol min-1 per g) at D 0.05 h-1 and 0.3 h-1. The aerobic fermentation of galactose occurred at D 0.275-0.3 h-1 which is identical to the results obtained in glucose-limited continuous cultures of this strain. Because galactose is not a repressing carbon source, this demonstrates that the Crabtree effect is not mediated by, or in any way related to glucose repression. Moreover, invertase and hexokinase I mRNA levels (both subject to glucose repression at the transcriptional level) were present when the yeast produced ethanol in galactose- and glucose-limited continuous cultures. In glucose-limited continuous cultures a decrease in alcohol dehydrogenase (I and II) mRNA levels and activity and phosphoglucomutase activity was observed with increasing dilution rates. In addition, at D 0.3 h-1, when the yeast produced ethanol, glucose-6-phosphate dehydrogenase and pyruvate decarboxylase were induced and a decrease in respiration was observed.(ABSTRACT TRUNCATED AT 250 WORDS)
Sierkstra
L N
LN
Department of Molecular Cell Biology, University of Utrecht, The Netherlands.
Nouwen
N P
NP
Verbakel
J M
JM
Verrips
C T
CT
D000332:Aerobiosis / Q000502:physiology; D003470:Culture Media; D004794:Enzyme Repression / Q000502:physiology; D005690:Galactose / Q000378:metabolism*; D015971:Gene Expression Regulation, Enzymologic / Q000502:physiology*; D015966:Gene Expression Regulation, Fungal / Q000502:physiology*; D005947:Glucose / Q000378:metabolism; D006019:Glycolysis / Q000502:physiology*; D012331:RNA, Fungal / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000201:enzymology*
D003470:Culture Media; D012331:RNA, Fungal; D012333:RNA, Messenger; D005947:Glucose; D005690:Galactose