The INACTIVATION OF THE TRANSPORT MECHANISM FOR Β‐GALACTOSIDES OF ESCHERICHIA COLI UNDER VARIOUS PHYSIOLOGICAL CONDITIONS

Koch, Arthur L.

doi:10.1111/j.1749-6632.1963.tb13663.x

Cited by 29 publications

(1 citation statement)

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“…Cells were harvested at various enzyme levels by adding 50 µg ml -1 chloramphenicol, after which the cells were spun and resuspended in M9 minimal medium containing 50 µg ml -1 chloramphenicol and carbon source, namely 0.4 % glycerol (absence of glucose) or 0.4 % glucose (presence of glucose) to obtain the experimental suspensions that were subsequently used to estimate the lactose permease and -galactosidase levels. Chloramphenicol, which inhibits not only protein synthesis but also degradation of permease molecules (Koch, 1963), was added to ensure that the enzyme levels did not change during the course of the experiment.…”

Section: Culturing Conditionsmentioning

confidence: 99%

Deconstructing glucose-mediated catabolite repression of thelacoperon ofEscherichia coli: I. Inducer exclusion, by itself, cannot account for the repression

Aggarwal

Narang

2019

Preprint

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The lac operon of Escherichia coli is repressed several 100-fold in the presence of glucose.This repression has been attributed to CRP-mediated transcriptional inhibition and EIIA Glcmediated inducer exclusion. The growing evidence against the first mechanism has led to the postulate that the repression is driven by inducer exclusion. The literature shows that in fully induced cells, inducer exclusion reduces the permease activity only 2-fold. However, it is conceivable that inducer exclusion drastically reduces the permease activity in partially induced cells. We measured the decline of lactose permease activity due to inducer exclusion in partially induced cells, but found that the permease activity decreased no more than 6-fold.We show that the repression is small because these experiments are performed in the presence of chloramphenicol. Indeed, when glucose is added to a culture growing on glycerol and TMG, but no chloramphenicol, lac is repressed 900-fold, of which inducer exclusion accounts for only 3-fold repression The remainder is due to reversal of the positive feedback loop, i.e., the decline of the intracellular TMG level leads to a lower permease level, which reduces the intracellular TMG level even further. The repression in the absence of chloramphenicol is therefore primarily due to positive feedback, which does not exist during measurements of inducer exclusion.

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Section: Culturing Conditionsmentioning

confidence: 99%