Dover S, Halpern Y S
J Bacteriol. 1972 Apr;110(1):165-70. doi: 10.1128/jb.110.1.165-170.1972.
Mutants of Escherichia coli K-12 isolated for their ability to utilize gamma-aminobutyrate (GABA) as the sole source of nitrogen exhibit a concomitant several-fold increase in the activities of gamma-aminobutyrate-alpha-ketoglutarate transaminase (GSST, EC 2.6.1.19) and succinic semialdehyde dehydrogenase (SSDH, EC 1.2.1.16). The increase in rate of enzymatic activity is not accompanied by any changes in the affinities of the mutant enzymes for their respective substrates. The synthesis of the two enzymes is highly coordinate under a great variety of conditions, in spite of the wide range of activities observed. In cultures grown in minimal media with ammonium salts as the source of nitrogen, both GSST and SSDH are severely repressed by glucose. Substitution of ammonia with GABA, glutamate, or aspartate greatly reduces the effect of glucose on the synthesis of the GABA utilization enzymes. This escape from catabolite repression is specific for GSST and SSDH and does not involve other enzymes sensitive to catabolite repression (e.g., beta-galactosidase, EC 3.2.1.23, and aspartase, EC 4.3.1.1).
因能够利用γ-氨基丁酸（GABA）作为唯一氮源而分离得到的大肠杆菌K-12突变体，其γ-氨基丁酸-α-酮戊二酸转氨酶（GSST，EC 2.6.1.19）和琥珀酸半醛脱氢酶（SSDH，EC 1.2.1.16）的活性同时会增加几倍。酶活性速率的增加并未伴随着突变酶对各自底物亲和力的任何变化。尽管观察到的活性范围很广，但在多种条件下，这两种酶的合成高度协调。在以铵盐作为氮源的基本培养基中生长的培养物中，GSST和SSDH都受到葡萄糖的严重抑制。用GABA、谷氨酸或天冬氨酸替代氨可大大降低葡萄糖对GABA利用酶合成的影响。这种对分解代谢物阻遏的逃避对GSST和SSDH具有特异性，且不涉及其他对分解代谢物阻遏敏感的酶（例如，β-半乳糖苷酶，EC 3.2.1.23，和天冬氨酸酶，EC 4.3.1.1）。
