Salmon‑GalNAc 

Salmon‑GalNAc (CAS 501432‑61‑7), systematically 6‑chloro‑3‑indolyl N‑acetyl‑β‑D‑galactosaminide, is a synthetic β‑N‑acetyl‑D‑galactosaminidase‑specific chromogenic substrate in which a 6‑chloro‑3‑indoxyl aglycone is linked via a β‑glycosidic bond to N‑acetyl‑D‑galactosamine (GalNAc). When hydrolyzed by β‑N‑acetyl‑D‑galactosaminidase or related β‑GalNAc‑cleaving enzymes, the indoxyl moiety is released and undergoes aerial oxidation to form an insoluble salmon‑colored indigo‑type precipitate, enabling clear visual detection of enzyme activity. This substrate is used in selective culture media to screen β‑GalNAcase‑producing microorganisms, in enzyme‑kinetic assays for recombinant or purified β‑N‑acetyl‑D‑galactosaminidases, and in histochemical staining for GalNAcase localization in glycoproteins and glycolipids. The salmon hue offers good contrast against background pigmentation, improving readability in dense platings or multiplex assays. Compared with traditional 4‑nitrophenyl‑N‑acetyl‑β‑D‑galactosaminide, Salmon‑GalNAc provides a chromogenic, solid‑medium‑compatible readout without the need for spectrophotometry. The compound is compatible with standard microbiological and biochemical buffers and is supplied as a research‑grade reagent.

Appearance

• Off‑white to pale yellow crystalline or lyophilized powder.
• Fine, free‑flowing texture suitable for accurate weighing and dissolution in aqueous or mixed aqueous‑organic solvents.

Source / synthesis

• Synthetically produced by coupling 6‑chloro‑3‑indoxyl with N‑acetyl‑β‑D‑galactosamine under glycosylation conditions to form the N‑acetyl‑β‑D‑galactosaminide derivative.
• Commercially manufactured by specialty enzyme‑substrate and biochemical suppliers (e.g., ChemicalBook, Sigma‑Aldrich‑type vendors, Biosynth) as a high‑purity, research‑use‑only reagent.

Molecular weight and structure

• Molecular formula: C16H19ClN2O6 (often listed as 6‑chloro‑3‑indoxyl‑N‑acetyl‑β‑D‑galactosaminide).
• Molecular weight: 370.78 g/mol.
• Structure: 6‑chloro‑1H‑indol‑3‑yl 2‑acetamido‑2‑deoxy‑β‑D‑galactopyranoside, with a β‑(1→4)‑type linkage between the indole C3‑O and the N‑acetyl‑D‑galactosamine ring.

Sugar specificity

• Specifically hydrolyzed by β‑N‑acetyl‑D‑galactosaminidases (β‑GalNAcase, EC 3.2.1.49) and related N‑acetyl‑β‑galactosaminide‑cleaving enzymes.
• Shows high selectivity over other β‑glycosidases and minimal cross‑reactivity when used under optimized assay conditions, making it suitable for probing GalNAc‑specific pathways.

Biological activity

• Acts as a chromogenic reporter for β‑N‑acetyl‑D‑galactosaminidase‑mediated hydrolysis of terminal N‑acetyl‑β‑D‑galactosaminyl linkages in glycoproteins, glycolipids, and oligosaccharides.
• Enzymatic cleavage yields 6‑chloro‑3‑indoxyl, which oxidizes and dimerizes into a salmon‑colored, water‑insoluble dye, providing a sensitive, low‑background readout for solid‑medium and solution‑based assays.

Purity and microbial contamination

• Typically supplied at ≥95–98% purity as determined by HPLC or similar analytical methods.
• Certificates of analysis and SDS‑type documents indicate acceptable levels of residual solvents, heavy‑metal content, and non‑sterile, low‑microbial‑contamination status suitable for microbiological and biochemical use.

Identity and quality control

• Identity inferred from molecular formula, molecular weight, NMR, HPLC, and spectral data, with reference to standard indolyl‑N‑acetyl‑β‑D‑hexosaminide profiles.
• Quality‑control procedures include checks for appearance, solubility, spectral characteristics, and performance in a defined β‑N‑acetyl‑D‑galactosaminidase activity assay system.

Shelf life and storage

• Shelf life is typically 12–24 months when stored as a dry powder at –20 °C in a tightly sealed container, protected from moisture and light.
• Aqueous or stock solutions should be prepared immediately before use or stored frozen for short periods to minimize degradation and nonspecific oxidation of the indoxyl moiety.

Application

• Screening and phenotypic differentiation of β‑N‑acetyl‑D‑galactosaminidase‑producing microorganisms on selective agar media.
• Enzyme‑activity assays for recombinant or purified β‑GalNAcases in solution or immobilized formats.
• Histochemical or cytochemical localization of β‑GalNAcase activity in tissue sections and glycan‑remodeling studies.

Key characteristics

• High sensitivity and low background due to formation of an insoluble salmon‑colored dye upon β‑N‑acetyl‑D‑galactosaminidase hydrolysis.
• Defined N‑acetyl‑β‑D‑galactosaminide linkage providing selectivity for β‑GalNAcase over other glycosidases.
• Crystalline, stable powder with a known molecular formula and weight, suitable for quantitative enzyme assays and standardized media formulations.

Citations

• ChemicalBook – 6‑Chloro‑3‑indoxyl‑N‑acetyl‑β‑D‑galactosaminide (Salmon‑GalNAc) entry: https://www.chemicalbook.com/ChemicalProductProperty_EN_CB32130160.htm
• eChemist (echemi.com) – 6‑Chloro‑3‑indoxyl‑N‑acetyl‑β‑D‑galactosaminide safety‑data sheet and CAS details: https://www.echemi.com/sds/6-chloro-3-indoxyl-n-acetyl-beta-d-galactosaminide-pd180521121189.html
• ChemDad – 6‑Chloro‑3‑indoxyl‑N‑acetyl‑β‑D‑galactosaminide product overview (use‑statement and handling context): https://www.chemdad.com/index.php?c=article&id=45307
• Sigma‑Aldrich – 4‑Nitrophenyl N‑acetyl‑β‑D‑galactosaminide product page (for N‑acetyl‑β‑D‑galactosaminidase‑substrate context and assay concepts): https://www.sigmaaldrich.com/US/en/product/sigma/n9003
• Biosynth – Salmon‑β‑D‑GalNAc technical‑document reference (6‑chloro‑3‑indolyl‑N‑acetyl‑β‑D‑galactosaminide, Salmon‑GalNAc): https://www.biosynth.com/Files/MSDS/EC/03/MSDS_EC03260_7000_ZH.pdf
• General glycosidase‑substrate overview (chromogenic and fluorogenic β‑GalNAcase substrates): https://www.medchemexpress.com/ (search for “N‑acetyl‑β‑D‑galactosaminidase substrate” or “Salmon‑GalNAc”)
• PubChem – 6‑Chloro‑3‑indolyl‑β‑D‑galactopyranoside entry (for 6‑chloro‑3‑indolyl‑β‑D‑hexoside dye‑chemistry reference): https://pubchem.ncbi.nlm.nih.gov/compound/6-Chloro-3-indolyl-beta-D-galactopyranoside
• Academic review on glycosidase substrates (N‑acetyl‑β‑D‑hexosaminidase and related systems): https://pmc.ncbi.nlm.nih.gov/ (search for “N‑acetyl‑β‑D‑hexosaminidase substrate”)
• Enzyme‑substrate catalog (indolyl‑type N‑acetyl‑β‑D‑galactosaminide substrates overview): https://www.chemicalbook.com/ (search for “6‑Chloro‑3‑indolyl‑N‑acetyl‑β‑D‑galactosaminide”)
• General glyco‑research‑supplier page (links to Salmon‑GalNAc and related glycosidase substrates): https://www.biosynth.com/ (search for “Salmon‑β‑D‑GalNAc” or “6‑chloro‑3‑indolyl‑N‑acetyl‑β‑D‑galactosaminide”)