Bell G, Payne G M, Payne J W
J Gen Microbiol. 1977 Feb;98(2):485-91. doi: 10.1099/00221287-98-2-485.
A new method has been developed for measuring peptide transport in aminoacid auxotrophs of Escherichia coli by following induction of beta-galactosidase. Appearance of the enzyme was determined after addition of inducer and peptides to amino-acid starved bacteria. For a given number of lysine equivalents, the rate and the extent of enzyme synthesis were the same for lysine and lysyl peptides; similar results were found for glycine and glycl peptides. Saturation constants for peptide transport were determined from the exogenous peptide concentration that gave half maximal rates of enzyme synthesis. The saturation constants, studies with mutants defective in peptide transport, and detection of competition between peptides for uptake, all endorsed earlier conclusions from growth tests about the structural specificities for peptide transport. The new method is quicker, more sensitive and more informative than growth tests.
已开发出一种新方法，通过追踪β-半乳糖苷酶的诱导来测量大肠杆菌氨基酸营养缺陷型中的肽转运。在向氨基酸饥饿的细菌中添加诱导剂和肽后，测定酶的出现情况。对于给定数量的赖氨酸当量，赖氨酸和赖氨酰肽的酶合成速率和程度相同；甘氨酸和甘氨酰肽也得到了类似的结果。肽转运的饱和常数由产生酶合成最大速率一半时的外源肽浓度确定。肽转运缺陷突变体的饱和常数研究以及肽摄取竞争的检测，均证实了早期生长试验关于肽转运结构特异性的结论。新方法比生长试验更快、更灵敏且信息量更大。
