Champney W S, Jensen R A
J Bacteriol. 1970 Oct;104(1):351-9. doi: 10.1128/jb.104.1.351-359.1970.
The biosynthetic pathway for tyrosine synthesis is regulated both by repression of enzyme synthesis and by feedback inhibition of enzyme activity in Bacillus subtilis. Nevertheless, wild-type cells produce significantly more tyrosine than is required for protein synthesis, and part of this is excreted into the medium. Alteration of nutritional and other environmental conditions of cultivation strongly influenced the amount of tyrosine excretion. The excretion of tyrosine by wild-type cells was compared with that of a regulatory mutant having a feedback-insensitive prephenate dehydrogenase. Tyrosine excretion varied directly with the in vitro activity of prephenate dehydrogenase and inversely with temperature in the two strains. The regulatory mutant excreted five times as much tyrosine as the wild type at all growth temperatures examined. The carbon source used for growth significantly influenced the level of tyrosine excretion. The specific activity of prephenate dehydrogenase was also affected by the carbon source. Incorporation studies with isotopic tyrosine and fluorometric determinations of tyrosine concentrations extractable in hot water were used to measure operationally the tyrosine pools in the mutant and wild-type strains. The effects of various environmental conditions on the synthesis and excretion of tyrosine led to the conclusion that metabolic controls governing end product contrations exist which are completely independent of regulation by feedback inhibition and repression.
在枯草芽孢杆菌中，酪氨酸合成的生物合成途径既受酶合成的阻遏调控，也受酶活性的反馈抑制调控。然而，野生型细胞产生的酪氨酸显著多于蛋白质合成所需的量，其中一部分会分泌到培养基中。培养的营养条件和其他环境条件的改变强烈影响酪氨酸的分泌量。将野生型细胞的酪氨酸分泌情况与具有反馈不敏感型预苯酸脱氢酶的调节突变体进行了比较。在这两种菌株中，酪氨酸分泌量与预苯酸脱氢酶的体外活性成正比，与温度成反比。在所检测的所有生长温度下，调节突变体分泌的酪氨酸量是野生型的五倍。用于生长的碳源显著影响酪氨酸的分泌水平。预苯酸脱氢酶的比活性也受碳源影响。利用同位素酪氨酸掺入研究以及对热水中可提取酪氨酸浓度的荧光测定，从操作上测量了突变体和野生型菌株中的酪氨酸库。各种环境条件对酪氨酸合成和分泌的影响得出结论：存在控制终产物浓度的代谢调控，这些调控完全独立于反馈抑制和阻遏调控。
