Analysis Of Saccharomyces Cerevisiae Metabliosm Under Conditions Of High Product Concentration

S.cerevisiae not only plays an important role in industrial application, but also becomes avery nice model organism for research in many areas. Nevertheless, the in vivo response toconditions of high concentration of the product and the Salt-stress conditions is still notclearly known. The research on which has always been a focus issue in theoretical or appliedstudy. The present study combine the approach of fermentation characteristics, enzyme assayand metabolic flux analysis to investigate the regulation of central carbon metabolism ofS.cerevisiae under conditions of high concentration of the product and the Salt-stressconditions.The enzyme activity of some key metabolic enzymes (pyruvate kinase,glucose-6-phosphate dehydrogenase, isocitrate dehydrogenase, malate dehydrogenase andethanol dehydrogenase) in Saccharomyces cerevisiae with YEPD medium were comparedwith malic aicd, citric acid and succinic acid mixed medium. The result showed that afteradding malic acid, enzymatic activity of pyruvate kinase、isocitrate dehydrogenase、malatedehydrogenase and ethanol dehydrogenase respectively declined34.82%,57.23%,39.15%and12.10%; after adding citric acid, enzymatic activity of pyruvate kinase、isocitratedehydrogenase and malate dehydrogenase respectively declined50.17%、42.20%and48.40%;after adding succinic acid, enzymatic activity of pyruvate kinase、glucose-6-phosphatedehydrogenase、isocitrate dehydrogenase、malate dehydrogenase and ethanol dehydrogenaserespectively declined34.16%,34.16%,50.87%,50.87%and12.37%. Pyruvate kinase、isocitrate dehydrogenase and malate dehydrogenase had bad tolerance to three kinds oforganic acids, tolerance of glucose-6-phosphate dehydrogenase and ethanol dehydrogenase tothree kinds of organic acids had selectivity.The method by calculating the metabolic flux was studied in Saccharomyces cerevisiaemetabolism under salt stress conditions. The result showed that under salt stress, the contentof trehalose, glycerol, ethanol and lactate was increased by24.44%,60.89%,23.32%and26.76%, respectively, the content of citrate, succinate, fumarate was decreased by82.11%, 50.37%and53.33%, respectively. The metabolic flux analysis indicates that the metabolicproduct flux of each branch channel in EMP is raised at the culture condition of the salt stress,in contrast, each metabolic flux of TCA cycle is reduced.The enzyme activity of some key metabolic enzymes (pyruvate kinase,glucose-6-phosphate dehydrogenase, isocitrate dehydrogenase, isocitrate lyase, malatedehydrogenase and ethanol dehydrogenase) in Saccharomyces cerevisiae under differentconditions of ethanol concentration, Preliminary study of these types of enzymes for ethanoltolerance. The result showed that exogenous ethanol added to make pyruvate kinase, isocitratedehydrogenase, alcohol dehydrogenase activity reduced, these three enzymes have a lesstolerance to elcohol. With increasing concentrations of exogenous ethanol, malatedehydrogenase and isocitrate lyase activity increased by a big margin, glucose-6-phosphatedehydrogenase activity increased slightly, these three enzymes have a strong tolerance toethanol, the effects of ethanol on yeast cells can promote the role of these three enzymes, Canstimulate the activity of these three enzymes. Exogenous ethanol can inhibit pyruvate kinasein the emp pathway, can stimulate glucose-6-phosphate dehydrogenase activity in the pentosephosphate pathway, can stimulate malate dehydrogenase activity in the TCA cycle, makeisocitrate metabolism by isocitrate lyase.