X-GlcA Sodium Salt: β-Glucuronidase Substrate for Research

5-Bromo-4-chloro-3-indolyl β-D-Glucuronide Sodium Salt [for Biochemical Research] (X-GlcA Sodium Salt) is a water-soluble chromogenic substrate that produces an intense, insoluble blue indigo precipitate upon enzymatic cleavage by β-glucuronidase (GUS), enabling sensitive, in situ visualization of GUS reporter gene expression, glucuronidase activity in histochemical preparations, and microbial identification assays.

Full IUPAC Name

Sodium (2S,3S,4S,5R,6S)-3,4,5-trihydroxy-6-[(5-bromo-4-chloro-1H-indol-3-yl)oxy]-tetrahydro-2H-pyran-2-carboxylate

Common Synonym

X-GlcA Sodium Salt; X-Glucuronide Sodium Salt

Aladdin SKU

B152261

Enzyme Target

β-D-Glucuronidase (GUS; EC 3.2.1.31)

Detection Signal

Insoluble blue indigo precipitate at site of enzymatic activity

Solubility

Water-soluble sodium salt form; facilitates preparation of aqueous assay buffers

Application Scope

GUS reporter gene assays, plant histochemistry, microbial identification, enzyme activity staining

What Is X-GlcA Sodium Salt and How Does It Work?

5-Bromo-4-chloro-3-indolyl β-D-Glucuronide Sodium Salt, universally abbreviated as X-GlcA Sodium Salt, is a synthetic chromogenic substrate designed for the detection and localization of β-D-glucuronidase (GUS; EC 3.2.1.31). The compound belongs to the well-established halogenated indolyl glycoside family of chromogenic substrates, which includes the widely used X-Gal for β-galactosidase detection.

The mechanism of signal generation is a two-step process. First, β-glucuronidase hydrolyzes the glucuronide bond between the indolyl moiety and the glucuronic acid sugar, releasing 5-bromo-4-chloro-3-hydroxyindole. Second, this unstable intermediate spontaneously oxidizes and dimerizes in the presence of atmospheric oxygen to form an intensely colored, water-insoluble blue indigo dye that precipitates at the exact site of enzymatic activity. This localized, stable precipitate makes X-GlcA Sodium Salt particularly valuable for in situ histochemical staining where precise spatial resolution of enzyme activity is required.

The sodium salt form confers improved aqueous solubility compared to the free acid form, simplifying stock solution preparation and ensuring homogeneous distribution within assay buffers.

Key Research Applications

GUS Reporter Gene Assays in Plant Biology: The GUS reporter system (uidA gene from Escherichia coli) is one of the most extensively used reporter systems in plant molecular biology. X-GlcA Sodium Salt is the standard chromogenic substrate for histochemical GUS assays, enabling researchers to map promoter activity, monitor transgene expression patterns, and track cell-specific gene regulation with high spatial resolution in plant tissues, seeds, and embryos.

Microbial Identification and Screening: β-Glucuronidase activity is a key biochemical marker used to distinguish certain bacterial species. Notably, Escherichia coli and several other coliforms express constitutive GUS activity, while many other organisms do not. X-GlcA can be incorporated into selective culture media or direct assay formats to rapidly identify GUS-positive organisms, supporting environmental microbiology, food safety testing, and clinical diagnostic research applications.

Enzyme Histochemistry: In mammalian tissue sections, endogenous β-glucuronidase activity is associated with lysosomes and is elevated in certain pathological conditions. X-GlcA Sodium Salt enables histochemical visualization of this endogenous enzyme activity, supporting studies in cell biology and pathology.

Enzyme Kinetics and Biochemical Characterization: X-GlcA can be used in solution-based spectrophotometric or visual assays to characterize β-glucuronidase enzyme kinetics, inhibitor screening, and substrate specificity studies.

Preparation, Handling, and Storage Guidelines

Stock Solution Preparation: Due to its sodium salt form, X-GlcA Sodium Salt dissolves readily in distilled or deionized water or aqueous buffer systems. A common approach is to prepare a concentrated stock solution (e.g., 20–100 mM) in water or dimethylformamide (DMF)/dimethyl sulfoxide (DMSO) for long-term storage, then dilute into the working assay buffer immediately before use. Researchers should verify solubility in their specific buffer system, particularly at higher concentrations.

Working Assay Conditions: For GUS histochemical staining, X-GlcA is typically used in a phosphate or sodium phosphate buffer at a mildly acidic to neutral pH (commonly pH 7.0–7.2), supplemented with potassium ferricyanide and potassium ferrocyanide to accelerate oxidative dimerization and improve spatial resolution of the blue precipitate. Incubation conditions, including time and temperature, should be optimized empirically for each tissue type and expression level.

Storage: The compound should be stored protected from light and moisture, at low temperature (typically −20 °C), in a tightly sealed container. Avoid repeated freeze-thaw cycles of stock solutions. Specific storage conditions should be confirmed from the product datasheet supplied with lot B152261.

Safety: Handle according to standard laboratory chemical safety practices. Consult the Safety Data Sheet (SDS) for B152261 before use. The halogenated indolyl compounds should be treated as potentially hazardous; avoid inhalation of dust and contact with skin and eyes.

Advantages Over Alternative Substrates

Superior Chromogenic Signal: The 5-bromo-4-chloro substitution pattern on the indole ring produces one of the most intensely colored blue indigo precipitates among chromogenic indolyl substrates, enabling detection of low-level GUS expression that might be missed with less sensitive substrates such as 5-bromo-3-indolyl glucuronide (X-Gluc without the 4-chloro substituent).

In Situ Localization: Unlike fluorometric substrates such as 4-methylumbelliferyl-β-D-glucuronide (MUG), which release a soluble fluorescent product that diffuses away from the site of hydrolysis, X-GlcA generates an insoluble precipitate that remains anchored at the enzymatic site. This makes X-GlcA the substrate of choice when cellular or tissue-level spatial resolution is needed.

Water Solubility: The sodium salt formulation ensures good aqueous solubility, avoiding the need for large volumes of organic co-solvents that might compromise tissue morphology or enzyme activity in histochemical protocols.

Compatibility with Counterstaining: The stable blue indigo precipitate is compatible with a range of histological counterstains (e.g., Nuclear Fast Red, Safranin), facilitating co-visualization of tissue architecture alongside GUS signal.

Ordering Information and Quality Assurance

X-GlcA Sodium Salt is available from Aladdin Scientific under SKU B152261. The product is supplied for biochemical research use only and is not intended for diagnostic or therapeutic applications in humans or animals.

Each lot of B152261 is manufactured and quality-controlled to meet the rigorous purity standards required for reliable biochemical assay performance. Researchers are advised to request the Certificate of Analysis (CoA) for their specific lot to confirm purity, identity (e.g., by HPLC, NMR, or mass spectrometry), and other critical quality attributes before use in sensitive assays.

For bulk quantities, custom packaging, or additional technical support regarding assay optimization with B152261, contact Aladdin Scientific's technical support team. Full safety and handling information is provided in the product Safety Data Sheet (SDS), available upon request or on the Aladdin Scientific website.

Frequently asked questions

What enzyme does X-GlcA Sodium Salt detect, and what signal does it produce?

X-GlcA Sodium Salt is a chromogenic substrate for β-D-glucuronidase (GUS; EC 3.2.1.31). Upon enzymatic hydrolysis, the released indolyl intermediate oxidizes and dimerizes to form an insoluble, intensely blue indigo precipitate at the site of enzyme activity, enabling straightforward visual or light-microscopic detection.

How does X-GlcA differ from MUG (4-methylumbelliferyl-β-D-glucuronide) for GUS detection?

MUG is a fluorometric substrate that releases a soluble fluorescent product (4-methylumbelliferone), which diffuses from the hydrolysis site, making it suitable for quantitative solution assays but not for spatial localization. X-GlcA produces an insoluble blue precipitate that remains anchored at the site of enzymatic activity, making it the preferred choice for in situ histochemical staining and tissue-level localization of GUS expression.

What buffer conditions are recommended for histochemical GUS staining with X-GlcA?

A common working solution uses X-GlcA dissolved in sodium phosphate buffer at approximately pH 7.0–7.2, supplemented with potassium ferricyanide and potassium ferrocyanide to promote oxidative dimerization and sharpen signal localization. Exact concentrations of all components, incubation time, and temperature should be optimized for the specific tissue type and GUS expression level being studied.

How should X-GlcA Sodium Salt (B152261) stock solutions be stored?

Stock solutions should be stored at −20 °C, protected from light and moisture, in tightly sealed containers. Repeated freeze-thaw cycles should be avoided to preserve substrate integrity. Always verify specific storage requirements from the lot Certificate of Analysis or product datasheet for B152261.

Is X-GlcA Sodium Salt suitable for use in microbial identification?

Yes. β-Glucuronidase activity is a key biochemical marker for identifying certain bacterial species, including Escherichia coli, which constitutively expresses GUS activity. X-GlcA can be incorporated into selective media or direct assay formats to enable rapid colorimetric identification of GUS-positive organisms, supporting applications in environmental microbiology and food safety research.

References

1. Jefferson RA, Kavanagh TA, Bevan MW. GUS fusions: beta-glucuronidase as a sensitive and versatile gene fusion marker in higher plants. EMBO J. 1987;6(13):3901-3907. PMID:3327686
2. Stomp AM. Histochemical localization of beta-glucuronidase. In: Gallagher SR, ed. GUS Protocols: Using the GUS Gene as a Reporter of Gene Expression. Academic Press; 1992:103-113.
3. Blumenthal A, Lund PA. Chromogenic substrates for the detection of microbial enzyme activities. Methods Microbiol. General reference on chromogenic substrates in microbiology.

Products are supplied for research and development use only. Not for use in humans, animals, diagnosis, or therapy.