Lin Wun-Yuan, Chang Jui-Yun, Hish Chih-Hsuan, Pan Tzu-Ming
Department of Food Science, Nutrition, and Nutraceutical Biotechnology, Shih Chien University, Taipei, Taiwan.
J Agric Food Chem. 2008 Jan 23;56(2):433-41. doi: 10.1021/jf072420e. Epub 2007 Dec 21.
Monascus species have the unique ability to economically produce many secondary metabolites. However, the influence of nitrogen limitation on Monascus secondary metabolite production and metabolic performance remains unclear. Varying the carbon/nitrogen (C/N) ratios in the range from 20 to 60 in cultivation of Monascus pilosus by glucose nitrate medium, our resulting data showed that red pigment production was significantly suppressed and more sensitive to nitrogen limitation than cellular biomass growth at a C/N ratio of 60. Using a comparative proteomic approach, combining two-dimensional gel electrophoresis, matrix-assisted laser desorption ionization time-of-flight/time-of-flight liquid chromatography-mass spectrometry, and tandem mass spectrometry, proteins with modified expression in the nitrogen-limited (C/N ratio 60) Monascus filamentous cells were identified. The results revealed that the deregulated proteins identified were involved in amino acid biosynthesis, protein translation, antioxidant-related enzymes, glycolysis, and transcriptional regulation. The results suggested that, under nitrogen limitation-induced suppression of protein translation and of expression of the related energy-generating enzymes, nitrogen limitation induced a switch of metabolic flux from glycolysis to the tricarboxylic acid (TCA) cycle for maintaining cellular energy homeostasis, resulting in repression of the metabolic shift of the polyketide biosynthesis pathway for red pigment production.
红曲霉菌具有经济地产生多种次级代谢产物的独特能力。然而，氮限制对红曲霉菌次级代谢产物产量和代谢性能的影响仍不清楚。通过在葡萄糖硝酸盐培养基中培养毛红曲霉，将碳/氮（C/N）比在20至60的范围内变化，我们得到的数据表明，在C/N比为60时，红色素的产生受到显著抑制，并且比细胞生物量生长对氮限制更敏感。采用比较蛋白质组学方法，结合二维凝胶电泳、基质辅助激光解吸电离飞行时间/飞行时间液相色谱-质谱联用以及串联质谱，鉴定了在氮限制（C/N比60）的红曲霉菌丝状细胞中表达发生改变的蛋白质。结果显示，鉴定出的失调蛋白质涉及氨基酸生物合成、蛋白质翻译、抗氧化相关酶、糖酵解和转录调控。结果表明，在氮限制诱导的蛋白质翻译和相关能量产生酶表达受抑制的情况下，氮限制诱导代谢通量从糖酵解转向三羧酸（TCA）循环以维持细胞能量稳态，从而导致抑制用于红色素产生的聚酮生物合成途径的代谢转变。
