Huber R E, Lytton J, Fung E B
J Bacteriol. 1980 Feb;141(2):528-33. doi: 10.1128/jb.141.2.528-533.1980.
Several different strains of Escherichia coli were grown on a variety of carbon sources under various growth conditions. Lactose was added (usually at mid-log phase), and the concentrations of the products of beta-galactosidase action on this sugar (galactose, glucose, and allolactose) were determined at various times thereafter in the total culture and in the medium. It was found that with each strain, with all carbon sources, and under all of the conditions studied, a very large proportion of the products were found in the medium. Control studies were carried out which showed that these results were not artifacts of the method of separating the cells from the medium. The results also did not arise from the secretion of beta-galactosidase into the medium, from the diffusion of substrates and products into and out of the cells due to leaks in the membrane, or from faults in the method of sugar analysis. In addition, the results showed that there were very high levels of products inside the cells under the conditions used and that the efflux of the products was rapid. The efflux might be energetically advantageous to the cell as well as being a means of storing excess products until needed.
几种不同菌株的大肠杆菌在各种生长条件下于多种碳源上生长。添加乳糖（通常在对数中期），此后在不同时间测定β-半乳糖苷酶作用于这种糖的产物（半乳糖、葡萄糖和别乳糖）在总培养物和培养基中的浓度。结果发现，对于每种菌株、所有碳源以及所有研究条件，很大一部分产物存在于培养基中。进行的对照研究表明，这些结果并非细胞与培养基分离方法造成的假象。这些结果也不是由于β-半乳糖苷酶分泌到培养基中、由于膜泄漏导致底物和产物进出细胞的扩散或糖分析方法的缺陷所致。此外，结果表明在所使用的条件下细胞内产物水平非常高，并且产物的外排很快。外排可能对细胞在能量方面有利，同时也是一种在需要之前储存过量产物的方式。
