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Isopropyl β-D-1-thiogalactopyranoside
Isopropyl β-D-1-thiogalactopyranoside (IPTG) is a molecular biology reagent. This compound is a molecular mimic of allolactose, a lactose metabolite that triggers transcription of the ''lac'' operon, and it is therefore used to induce protein expression where the gene is under the control of the lac operator.
IPTG, unlike allolactose, is not hydrolyzable by β-galactosidase, its concentration therefore remains constant in an experiment. For induction, a sterile, filtered 1 M solution of IPTG is typically added by 1:1000 dilution into a logarithmically growing bacterial culture, however, different final concentration of IPTG may also be used.
==Mechanism of action==
Like allolactose, IPTG binds to the lac repressor and releases the tetrameric repressor from the lac operator in an allosteric manner, thereby allowing the transcription of genes in the lac operon, such as the gene coding for beta-galactosidase, a hydrolase enzyme that catalyzes the hydrolysis of β-galactosides into monosaccharides. But unlike allolactose, the sulfur (S) atom creates a chemical bond which is non-hydrolyzable by the cell, preventing the cell from metabolizing or degrading the inducer. The concentration of IPTG therefore remains constant and the expression of ''lac p/o''-controlled genes would not be inhibited during the experiment.
IPTG uptake by ''E. coli'' can be independent of the action of lactose permease, since other transport pathways are also involved. At low concentration, IPTG enters cells through lactose permease, but at high concentrations (typically used for protein induction), IPTG can enter the cells independently of lactose permease.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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