详细解释：
| Studies on regulation of the biosynthesis of aromatic amino acids in Str. caespitosus showed that DAHP synthase, the first enzyme of the pathway, had no isoenzyme. Its specific activity could be increased by nitrate. It was not repressed by L-Trp. The enzyme was strongly feedback inhibited by L-Trp but not affected by L-Tyr and L-Phe. The inhibition of L-Trp was noncompetitive with respect to E4P. Km values for PEP and E4P were 50 and 100μmol/L, respectively. The enzyme could be stabilized by PEP and ... |
| 对头状轮生链霉菌(Streptoverticillium caespitosus)芳香氨基酸合成途径的研究表明,第一个酶即3—脱氧—α—阿拉伯庚酮糖-7-磷酸(DAHP)合成酶无同工酶,不被L-色氨酸阻遏,比活力可被硝酸盐促进。L-色氨酸强烈地反馈抑制此酶,L-酪氨酸和L-苯丙氨酸无作用。L-色氨酸的反馈抑制对磷酸烯醇式丙酮酸(PEP)是非竞争性的,K_i为373μmol/L。酶对PEP和4-磷酸亦藓糖(E4P)的K_m值分别为50和100μmol/L。PEP和C0~(2+)对酶有稳定作用。邻氨基苯甲酸合成酶活力可被1mmol/L L-色氨酸完全抑制,此酶也受L-色氨酸的阻遏,但是色氨酸支路上其余4个酶不被阻遏。分支酸变位酶被L-酪氨酸抑制。L-苯丙氨酸抑制预苯酸脱水酶,并更强地抑制预苯酸脱氢酶。 |
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