Isopropyl β--1-thiogalactopyranoside (IPTG) is a

molecular biology Molecular biology is a branch of biology that seeks to understand the molecule, molecular basis of biological activity in and between Cell (biology), cells, including biomolecule, biomolecular synthesis, modification, mechanisms, and interactio ...

reagent. This compound is a molecular mimic of allolactose, a

lactose Lactose is a disaccharide composed of galactose and glucose and has the molecular formula C12H22O11. Lactose makes up around 2–8% of milk (by mass). The name comes from (Genitive case, gen. ), the Latin word for milk, plus the suffix ''-o ...

metabolite In biochemistry, a metabolite is an intermediate or end product of metabolism. The term is usually used for small molecules. Metabolites have various functions, including fuel, structure, signaling, stimulatory and inhibitory effects on enzymes, c ...

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.

Mechanism of action

Like allolactose, IPTG binds to the lac repressor and releases the tetrameric repressor from the lac operator in an

allosteric In the fields of biochemistry and pharmacology an allosteric regulator (or allosteric modulator) is a substance that binds to a site on an enzyme or receptor distinct from the active site, resulting in a conformational change that alters the p ...

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 In molecular biology, an inducer is a molecule that regulates gene expression. An inducer functions in two ways; namely: *By disabling repressors. The gene is expressed because an inducer binds to the repressor. The binding of the inducer to the r ...

. Therefore, its concentration remains constant during an 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.

Use in laboratory

When stored as a powder at 4 °C or below, IPTG is stable for 5 years. It is significantly less stable in solution;

Sigma Sigma ( ; uppercase Σ, lowercase σ, lowercase in word-final position ς; ) is the eighteenth letter of the Greek alphabet. In the system of Greek numerals, it has a value of 200. In general mathematics, uppercase Σ is used as an operator ...

recommends storage for no more than a month at room temperature. IPTG is an effective inducer of protein expression in the concentration range of 100 μmol/L to 3.0

mmol/L Molar concentration (also called molarity, amount concentration or substance concentration) is the number of moles of solute per liter of solution. Specifically, It is a measure of the concentration of a chemical species, in particular, of a sol ...

. Typically, a sterile, filtered 1 mol/L solution of IPTG is added 1:1000 to an exponentially growing bacterial culture, to give a final concentration of 1 mmol/L. The concentration used depends on the strength of induction required, as well as the genotype of cells or plasmid used. If ''lacI^q'', a mutant that over-produces the lac repressor, is present, then a higher concentration of IPTG may be necessary. In blue-white screen, IPTG is used together with X-gal. Blue-white screen allows colonies that have been transformed with the recombinant plasmid rather than a non-recombinant one to be identified in cloning experiments.https://www.agilent.com/Library/usermanuals/Public/200521.pdf

References

External links

IPTG bound to proteins
in the PDB {{DEFAULTSORT:Isopropyl B-D-1-thiogalactopyranoside Carbohydrates Molecular biology Isopropyl compounds Organosulfur compounds