MECHANISM OF CATABOLITE REPRESSION OF TRYPTOPHANASE SYNTHESIS IN ESCHERICHIA-COLI
MECHANISM OF CATABOLITE REPRESSION OF TRYPTOPHANASE SYNTHESIS IN ESCHERICHIA-COLI
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DOI：
10.1099/13500872-140-8-2125
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发表时间：
1994-08-01
期刊：
影响因子：
--
通讯作者：
SAIER, MH
中科院分区：
文献类型：
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作者：
ISAACS, H;CHAO, D;SAIER, MH
利用一系列缺乏环AMP磷酸二酯酶并改变磷酸烯醇丙酮酸的两种蛋白质：糖磷酸转移酶系统（PTS）酶I和斯坦福大学酶IIA（Glc）的大肠杆菌等基因菌株，研究了葡萄糖及其非代谢类似物甲基α-葡萄糖苷对色氨酸吲哚裂解酶（色氨酸吲哚裂解酶）的抑制作用。通过在生长培养基中加入葡萄糖，可以轻度抑制葡聚糖酶的基础活性，但诱导型葡聚糖酶合成在亲本菌株中受到强烈的葡萄糖抑制，其表现出正常的PTS酶活性。甲基α-葡萄糖苷在该菌株中没有影响。酶I的丧失降低了对葡萄糖阻遏的敏感性，但增强了对甲基α-葡糖苷阻遏的敏感性。酶IIA（Glc）活性的丧失在很大程度上消除了甲基α-葡萄糖苷的抑制作用，但对葡萄糖抑制的影响不太严重。这两种糖的阻遏作用完全逆转列入环AMP在生长培养基中。色氨酸摄取在相同的条件下被抑制弱葡萄糖和更强烈的甲基α-葡萄糖苷在亲本菌株。酶I的部分损失减轻了两种糖的抑制作用。甲基α-葡萄糖苷的抑制作用似乎主要是由于能量竞争，而不是负责阻遏的葡聚糖酶的合成。测量环AMP的净生产以及环AMP的细胞内浓度显示了良好的相关性与镇压的强度。结果表明，虽然基础的糖苷酶的合成是相对不敏感的分解代谢产物的镇压，诱导合成受到强烈的镇压由两个不同的机制，一个依赖于酶IIA（葡萄糖）的PTS和其他独立的这种蛋白质。这两种机制都可归因于环AMP合成的抑制率。没有证据表明，一个环AMP的独立机制的分解代谢产物的镇压。
Repression of tryptophanase (tryptophan indole-lyase) by glucose and its nonmetabolizable analogue methyl alpha-glucoside has been studied employing a series of isogenic strains of Escherichia coli lacking cyclic AMP phosphodiesterase and altered for two of the proteins of the phosphoenolpyruvate :sugar phosphotransferase system (PTS), Enzyme I and University, Stanford, Enzyme IIA(Glc). Basal activity of tryptophanase was depressed mildly by inclusion of glucose in the growth medium, but inducible tryptophanase synthesis was subject to strong glucose repression in the parental strain, which exhibited normal PTS enzyme activities. Methyl alpha-glucoside was without effect in this strain. Loss of Enzyme I decreased sensitivity to repression by glucose but enhanced sensitivity to repression by methyl alpha-glucoside. Loss of Enzyme IIA(Glc) activity largely abolished repression by methyl alpha-glucoside but had a less severe effect on glucose repression. The repressive effects of both sugars were fully reversed by inclusion of cyclic AMP in the growth medium. Tryptophan uptake under the same conditions was inhibited weakly by glucose and more strongly by methyl alpha-glucoside in the parental strain. Inhibition by both sugars was alleviated by partial loss of Enzyme I. Inhibition by methyl alpha-glucoside appeared to be largely due to energy competition and was not responsible for repression of tryptophanase synthesis. Measurement of net production of cyclic AMP as well as intracellular concentrations of cyclic AMP revealed a good correlation with intensity of repression. The results suggest that while basal tryptophanase synthesis is relatively insensitive to catabolite repression, inducible synthesis is subject to strong repression by two distinct mechanisms, one dependent on enzyme IIA(Glc) of the PTS and the other independent of this protein. Both mechanisms are attributable to depressed rates of cyclic AMP synthesis. No evidence for a cyclic-AMP-independent mechanism of catabolite repression was obtained.