Isopropyl-beta-D-thiogalactopyranoside
[CAS# 367-93-1]

Identification

• Classification: Biochemical >> Carbohydrate >> Monosaccharide
• Name: Isopropyl-beta-D-thiogalactopyranoside
• Synonyms: IPTG; Isopropyl-beta-D-thiogalactoside
• Molecular Formula: C₉H₁₈O₅S
• Molecular Weight: 238.30
• CAS Registry Number: 367-93-1
• EC Number: 206-703-0
• SMILES: CC(C)S[C@H]1[C@@H]([C@H]([C@H]([C@H](O1)CO)O)O)O

Properties

• Melting point: 105 °C
• alpha: -31 ° (c=1, water)
• Water solubility: soluble

Safety Data

• Hazard Symbols: GHS07;GHS08 Warning
• Risk Statements: H302-H312-H315-H319-H332-H335-H351
• Safety Statements: P203-P261-P264-P264+P265-P270-P271-P280-P301+P317-P302+P352-P304+P340-P305+P351+P338-P317-P318-P319-P321-P330-P332+P317-P337+P317-P362+P364-P403+P233-P405-P501

Hazard Classification

Hazard	Class	Category Code	Hazard Statement
Specific target organ toxicity - single exposure	STOT SE	3	H335
Eye irritation	Eye Irrit.	2	H319
Skin irritation	Skin Irrit.	2	H315
Carcinogenicity	Carc.	2	H351
Acute toxicity	Acute Tox.	4	H332
Acute toxicity	Acute Tox.	3	H301
Eye irritation	Eye Irrit.	2A	H319
Acute toxicity	Acute Tox.	4	H312
Acute toxicity	Acute Tox.	4	H302
Acute toxicity	Acute Tox.	3	H311

Discovery and Applications

Isopropyl-β-D-thiogalactoside (IPTG) is a molecular biology reagent commonly used to induce gene expression. IPTG was discovered in the mid-20th century while studying the lactose operon, a gene regulatory system in Escherichia coli (E. coli). Researchers needed a compound that could effectively mimic the natural inducer of the lactose operon, allolactose, without being metabolized by the bacteria. IPTG was synthesized as a stable analog that binds to the lactose repressor, relieving its repression and allowing gene transcription.

The chemical formula of IPTG is C9H18O5S. It is a colorless crystalline solid that is highly soluble in water. The structure of IPTG includes a galactoside ring with an isopropyl group and a sulfur atom, mimicking the structure of allolactose. Unlike allolactose, IPTG is not a substrate for β-galactosidase, which means that it is not hydrolyzed by the enzyme, allowing it to continuously induce gene expression without being depleted.

IPTG works by binding to the lactose repressor protein, causing a conformational change that releases the repressor from the operator region of the lactose operon. This derepression enables RNA polymerase to transcribe downstream genes, thereby producing the proteins encoded by these genes. The consistency and non-metabolizable nature of IPTG ensures continuous induction of gene expression.

IPTG is widely used to induce the expression of genes cloned under the control of the lactose operon promoter. This is particularly useful in the production of recombinant proteins. By adding IPTG to the culture medium, researchers can control the timing and level of protein expression to obtain high yields of the desired protein.

IPTG is used in blue-white screening, a method for identifying recombinant bacterial colonies. Bacteria are grown on agar plates containing IPTG and X-gal. Colonies expressing β-galactosidase (indicating the presence of the lacZ gene) convert X-gal to a blue product. Recombinant colonies that have disrupted the lacZ gene remain white and are easily distinguishable.

IPTG is used in functional genomics to study gene function and regulation. By inducing or repressing specific genes, researchers can observe the resulting phenotypic changes and gain insight into gene function and interactions.

IPTG is less toxic, but should still be handled with care. Standard laboratory safety procedures should be followed, such as wearing gloves and goggles. IPTG solutions should be freshly prepared or stored at -20°C to maintain stability and effectiveness.

References

2020. IPTG in Protein Expression. Protein Expression and Purification, 172.
DOI: 10.1016/j.pep.2020.105645