During the initiation of fermentation overexpression of hexokinase PII in yeast transiently causes a similar deregulation of glycolysis as deletion of Tps1.
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1998
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In the yeast Saccharomyces cerevisiae a novel control exerted by TPS1 (=GGS1=FDP1=BYP1=CIF1
=GLC6=TSS1)-encoded trehalose-6-phosphate synthase, is essential for restriction of glucose influx into glycolysis
apparently by inhibiting hexokinase activity in vivo. We show that up to 50-fold overexpression of hexokinase does
not noticeably affect growth on glucose or fructose in wild-type cells. However, it causes higher levels of
glucose-6-phosphate, fructose-6-phosphate and also faster accumulation of fructose-1,6-bisphosphate during the
initiation of fermentation. The levels of ATP and Pi correlated inversely with the higher sugar phosphate levels. In
the first minutes after glucose addition, the metabolite pattern observed was intermediate between those of the tps1Ä
mutant and the wild-type strain. Apparently, during the start-up of fermentation hexokinase is more rate-limiting
in the first section of glycolysis than phosphofructokinase. We have developed a method to measure the free
intracellular glucose level which is based on the simultaneous addition of D-glucose and an equal concentration of
radiolabelled L-glucose. Since the latter is not transported, the free intracellular glucose level can be calculated as the
difference between the total D-glucose measured (intracellular+periplasmic/extracellular) and the total L-glucose
measured (periplasmic/extracellular). The intracellular glucose level rose in 5 min after addition of 100 mM-glucose
to 0·5–2 mM in the wild-type strain, &10 mM in a hxk1Ä hxk2Ä glk1Ä and 2–3 mM in a tps1Ä strain. In the strains
overexpressing hexokinase PII the level of free intracellular glucose was not reduced. Overexpression of hexokinase
PII never produced a strong effect on the rate of ethanol production and glucose consumption. Our results show that
overexpression of hexokinase does not cause the same phenotype as deletion of Tps1. However, it mimics it
transiently during the initiation of fermentation. Afterwards, the Tps1-dependent control system is apparently able
to restrict properly up to 50-fold higher hexokinase activity.
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ERNANDES, J. R. et al. During the initiation of fermentation overexpression of hexokinase PII in yeast transiently causes a similar deregulation of glycolysis as deletion of Tps1. Yeast, Amsterdam, v. 14, p. 255-269, 1998. Disponível em: <http://onlinelibrary.wiley.com/doi/10.1002/(SICI)1097-0061(199802)14:3%3C255::AID-YEA228%3E3.0.CO;2-N/epdf>. Acesso em: 10 jan. 2017.