Oxygen- and growth rate-dependent regulation of Escherichia coli fumarase (FumA, FumB, and FumC) activity
Oxygen- and growth rate-dependent regulation of Escherichia coli fumarase (FumA, FumB, and FumC) activity
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DOI：
10.1128/jb.183.2.461-467.2001
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发表时间：
2001-01-01
影响因子：
3.2
通讯作者：
Kuo, JT
中科院分区：
文献类型：
--
作者：
Tseng, CP;Yu, CC;Kuo, JT
大肠杆菌含有三种生物化学性质不同的脱氢酶，它们催化三羧酸循环中富马酸转化为L-苹果酸。分批培养研究表明，脱氢酶活性根据碳底物和细胞倍增时间而变化。在野生型和突变体中的生长速率控制的FumA和FumC活性的连续培养证明，诱导四至五倍时，细胞生长速率（k）从1.2/h降低到0.24/h，在1和21%O-2，分别。当乙酸盐代替葡萄糖作为唯一碳源时，FumA和FumC活性有双重诱导作用。然而，这些酶活性仍显示出在生长速率控制下。进一步对cya突变体FumA和FumC活性的研究表明，生长速率对FumA酸FumC活性的控制是环磷酸腺苷依赖的。虽然总的酶活性在有氧条件下增加，但单个酶活性在不同氧水平下有所不同。虽然FumB活性在厌氧生长期间（k = 0.6/h）是最大的，但FumA是厌氧细胞生长下的主要酶，并且当氧升高至1至2%时达到最大活性。进一步增加氧水平导致高氧化态FumA和FumB活性失活，但当氧水平高于4%时，FumC活性同时增加。在突变体中也发现了响应于不同氧水平的酶活性的相同调节。因此，这三种酶的合成是根据细胞遇到的环境氧气以分级方式控制的。
Escherichia coli contains three biochemically distinct fumarases which catalyze the interconversion of fumarate to L-malate in the tricarboxylic acid cycle, Batch culture studies indicated that fumarase activities varied according to carbon substrate and cell doubling time. Growth rate control of fumarase activities in the wild type and mutants was demonstrated in continuous culture; FumA and FumC activities were induced four- to fivefold when the cell growth rate (k) was lowered from 1.2/h to 0.24/h at 1 and 21% O-2, respectively. There was a twofold induction of FumA and FumC activities when acetate was utilized instead of glucose as the sole carbon source. However, these fumarase activities were still shown to be under growth rate control. Thus, the activity of the fumarases is regulated by the cell growth rate and carbon source utilization independently, Further examination of FumA and FumC activities in a cya mutant suggested that growth rate control of FumA acid FumC activities is cyclic AMP dependent, Although the total fumarase activity increased under aerobic conditions, the individual fumarase activities varied under different oxygen levels. While FumB activity was maximal during anaerobic growth (k = 0.6/h), FumA was the major enzyme under anaerobic cell growth, and the maximum activity was achieved when oxygen was elevated to 1 to 2%. Further increase in the oxygen level caused inactivation of FumA and FumB activities by the high oxidized state, but FumC activity increased simultaneously when the oxygen level aas higher than 4%. The same regulation of the activities of fumarases in response to different oxygen levels was also found in mutants. Therefore, synthesis of the three fumarase enzymes is controlled in a hierarchical fashion depending on the environmental oxygen that the cell encounters.