Isopropyl β-D-1-thiogalactopyranoside


Colorless powder


110-112 ° C

Soluble in water

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Isopropyl- β -D-thiogalactopyranoside (IPTG ) is a galactose thioglycoside (S -glycoside ) which is used as an artificial inducer of the lactose operon in Escherichia coli.

Chemical and physical properties

The optical angle of rotation is -28.6 ° (589 nm, 20 ° C, 0.82 g / 100 mL H2O).

Biological Properties

IPTG acts as an activator (inductor) of the lac operon by binding ( the protein product of the lacI gene ) to the lac repressor. This results in an allosteric conformational change in the repressor that inhibits its interaction with the lac operators. In contrast to lactose or IPTG allolactose is not converted in the natural metabolism of bacteria, its concentration is therefore constant during a test, and the repressor is inactivated. Such nichtmetabolisierten inductors are called in the English jargon " gratuitous inducers " in German is less descriptive and not entirely true "artificial inducers ".


IPTG used in molecular biology to prepare recombinant proteins by expression of cloned genes. The desired gene is located here under the control of a regulated promoter of lac repressor. Such a promoter - gene fusion is usually located on a plasmid are transformed with the bacteria. Is thus the gene is first turned off, and only by adding IPTG converted to protein ( transcription and translation ), the cells have to express the Lac repressor in sufficient quantities. Furthermore, it is often ( and mostly unnecessarily ) used in the blue - white selection. The multicopy plasmids used in this selection usually carry lac operators and thus titrate the few cellular Lac repressor molecules.