Stubbs J D, Stubbs E A
J Bacteriol. 1971 Dec;108(3):1181-91. doi: 10.1128/jb.108.3.1181-1191.1971.
Lysates of Escherichia coli Ymel obtained from cultures grown in the absence of tryptophan in minimal medium supplemented with 0.1% casein hydrolysate show an approximate fivefold increase in steady-state specific activity of both anthranilate synthetase and tryptophan synthetase A protein relative to cultures grown in nonsupplemented medium. In the presence of repressing levels of exogenous tryptophan, growth of cultures in casein hydrolysate-supplemented medium results in a noncoordinate enhancement of repression of 10-fold for anthranilate synthetase and twofold for tryptophan synthetase A protein. Similar, but less pronounced, effects are shown for strain W3110. Strains possessing tryptophan regulator gene mutations do not exhibit this first effect, but do yield an approximate twofold decrease in specific activity of both enzymes when grown in medium supplemented with tryptophan and casein hydrolysate. A stimulation of derepression of both enzymes in strain Ymel equivalent to that induced by casein hydrolysate can be reproduced by growth in minimal medium supplemented with threonine, phenylalanine, tyrosine, serine, glutamic acid, and glutamine. Doubling time in this medium is not significantly different from that in minimal medium. An enhancement of repression which partially mimics that observed on growth in medium supplemented with tryptophan plus casein hydrolysate is obtained when Ymel is grown on medium supplemented with tryptophan plus methionine. Threonine or phenylalanine plus tyrosine as separate medium supplements are independently capable of producing a 1.4-fold or 3.4-fold stimulation, respectively, but in combination only the phenylalanine plus tyrosine effect is manifested unless serine and glutamic acid or glutamine are included. Our data show that expression of the tryptophan biosynthetic enzymes can be significantly influenced in vivo as a result of growth in medium supplemented with a variety of amino acids.
从在添加了0.1%酪蛋白水解物的基本培养基中、于无色氨酸条件下培养所得的大肠杆菌Ymel裂解物中，邻氨基苯甲酸合成酶和色氨酸合成酶A蛋白的稳态比活性相对于在未添加培养基中培养的培养物而言，显示出约五倍的增加。在存在抑制水平的外源色氨酸时，在添加酪蛋白水解物的培养基中培养的培养物，会导致邻氨基苯甲酸合成酶的阻遏增强10倍，色氨酸合成酶A蛋白的阻遏增强两倍，二者表现出不协调的增强。菌株W3110表现出类似但不太明显的效应。具有色氨酸调节基因突变的菌株不表现出这种第一种效应，但在添加色氨酸和酪蛋白水解物的培养基中生长时，两种酶的比活性确实会降低约两倍。通过在添加苏氨酸、苯丙氨酸、酪氨酸、丝氨酸、谷氨酸和谷氨酰胺的基本培养基中生长，可以重现菌株Ymel中两种酶的去阻遏刺激，其程度与酪蛋白水解物诱导的相当。在此培养基中的倍增时间与在基本培养基中的没有显著差异。当Ymel在添加色氨酸加蛋氨酸的培养基上生长时，会获得部分模拟在添加色氨酸加酪蛋白水解物的培养基上生长时所观察到的阻遏增强。苏氨酸或苯丙氨酸加酪氨酸作为单独的培养基补充物分别能够产生1.4倍或3.4倍的刺激，但除非包含丝氨酸和谷氨酸或谷氨酰胺，否则只有苯丙氨酸加酪氨酸的效应会显现出来。我们的数据表明，由于在添加多种氨基酸的培养基中生长，色氨酸生物合成酶的表达在体内会受到显著影响。
