tailieunhanh - Báo cáo khoa học: A potential mechanism of energy-metabolism oscillation in an aerobic chemostat culture of the yeast Saccharomyces cerevisiae

The energy-metabolism oscillation in aerobic chemostat cultures of yeast is a periodic change of the respiro-fermentative and respiratory phase. In the respiro-fermentative phase, the NADH level was kept high and respiration was suppressed, and glucose was anabolized into trehalose and glycogen at a rate comparable to that of catabolism. | iFEBS Journal A potential mechanism of energy-metabolism oscillation in an aerobic chemostat culture of the yeast Saccharomyces cerevisiae Zhaojun Xu and Kunio Tsurugi Department of Biochemistry 2 University of Yamanashi Faculty of Medicine Tamaho Japan Keywords continuous culture dissipative structure energy-metabolism oscillation NADH trehalose Correspondence K. Tsurugi Department of Biochemistry 2 University of Yamanashi Faculty of Medicine 1110 Shimokato Tamaho Yamanashi 409-3898 Japan Tel Fax 81 55 2736784 E-mail ktsurugi@ Received 25 December 2005 revised 16 February 2006 accepted 27 February 2006 doi The energy-metabolism oscillation in aerobic chemostat cultures of yeast is a periodic change of the respiro-fermentative and respiratory phase. In the respiro-fermentative phase the NADH level was kept high and respiration was suppressed and glucose was anabolized into trehalose and glycogen at a rate comparable to that of catabolism. On the transition to the respiratory phase cAMP levels increased triggering the breakdown of storage carbohydrates and the increased influx of glucose into the glycolytic pathway activated production of glycerol and ethanol consuming NADH. The resulting increase in the NAD NADH ratio stimulated respiration in combination with a decrease in the level of ATP which was consumed mainly in the formation of biomass accompanying budding and the accumulated ethanol and glycerol were gradually degraded by respiration via NAD -dependent oxidation to acetate and the respiratory phase ceased after the recovery of NADH and ATP levels. However the mRNA levels of both synthetic and degradative enzymes of storage carbohydrates were increased around the early respiro-fermentative phase when storage carbohydrates are being synthesized suggesting that the synthetic enzymes were expressed directly as active forms while the degradative enzymes were activated late by cAMP. In summary the energy-metabolism