Aon M A, Mónaco M E, Cortassa S
Departamento de Bioquímica de la Nutrición, Facultad de Bioquímica, Química y Farmacia, Universidad Nacional de Tucumán, Argentina.
Exp Cell Res. 1995 Mar;217(1):42-51. doi: 10.1006/excr.1995.1061.
Cell proliferation arrest at 37 degrees C (restrictive temperature) of the cell division cycle (cdc) mutants of Saccharomyces cerevisiae cdc28, cdc35, cdc19, cdc21, and cdc17 was correlated with carbon and energy uncoupling. At 37 degrees C, cdc mutants diverted to biomass synthesis only 3 to 4% and 8 to 24% of the fluxes of carbon consumed and ATP obtained by catabolism, respectively, compared with 48 and 34% in the wild-type strain A364A. At the permissive temperature (25 degrees C), the wild type showed similar carbon and energy coupling indexes as at 37 degrees C. However, carbon and energy coupling indexes were two- to sevenfold higher at 25 degrees than at 37 degrees C in cdc mutants; e.g., at 25 degrees C two- to sevenfold higher amounts of carbon and ATP were directed to biomass production than at 37 degrees C. The wild-type strain exhibited a purely oxidative glucose catabolism at 37 degrees C (RQ approximately 1.0), while the cell proliferation arrest of cdc mutants at the same temperature was characterized by fermentative metabolism. At 37 degrees C, cdc mutants directed 50 to 60% of the carbon to ethanol production; 3 to 12% of the carbon was recovered as glycerol in cdc mutants as well as in the wild type. The proliferation arrest of the cell division cycle mutant cdc28 correlated with a significant decrease in the incorporation of radioactive precursors into DNA, RNA, and proteins. In the presence of 8-hydroxyquinoline, the wild-type strain underwent cell proliferation arrest and also exhibited metabolic uncoupling with bioenergetic and catabolic behavior similar to that of the cdc mutants at 37 degrees C. Experimental evidence obtained with cdc19, whose defective gene product is pyruvate kinase, suggests that the primary defect of cdc mutants correlates with a metabolically, highly uncoupled yeast cell. The results presented point to the existence of strong carbon and energy uncoupling together with cell division arrest exhibited by cdc mutants at the restrictive temperature. The degree of uncoupling appears to be tuned, at least in part, by the increase in flux of sugar catabolism through the ethanol fermentative pathway.
酿酒酵母cdc28、cdc35、cdc19、cdc21和cdc17的细胞分裂周期（cdc）突变体在37℃（限制温度）下的细胞增殖停滞与碳和能量解偶联相关。在37℃时，与野生型菌株A364A中分别为48%和34%相比，cdc突变体仅将分解代谢消耗的碳通量的3%至4%以及获得的ATP通量的8%至24%用于生物量合成。在允许温度（25℃）下，野生型显示出与37℃时相似的碳和能量偶联指数。然而，cdc突变体在25℃时的碳和能量偶联指数比在37℃时高2至7倍；例如，在25℃时，导向生物量生产的碳和ATP的量比在37℃时高2至7倍。野生型菌株在37℃时表现出纯氧化型葡萄糖分解代谢（呼吸商约为1.0），而cdc突变体在相同温度下的细胞增殖停滞以发酵代谢为特征。在37℃时，cdc突变体将50%至60%的碳导向乙醇生产；在cdc突变体以及野生型中，3%至12%的碳以甘油形式回收。细胞分裂周期突变体cdc28的增殖停滞与放射性前体掺入DNA、RNA和蛋白质的显著减少相关。在8 - 羟基喹啉存在下，野生型菌株经历细胞增殖停滞，并且还表现出代谢解偶联，其生物能量和分解代谢行为类似于cdc突变体在37℃时的行为。用cdc19获得的实验证据表明，其缺陷基因产物是丙酮酸激酶，这表明cdc突变体的主要缺陷与代谢高度解偶联的酵母细胞相关。所呈现的结果表明，在限制温度下，cdc突变体存在强烈的碳和能量解偶联以及细胞分裂停滞。解偶联程度似乎至少部分地由通过乙醇发酵途径的糖分解代谢通量增加所调节。
