Inosine

Technical Specifications

Product Description & Scientific Applications

Inosine (hypoxanthine 9-β-D-ribofuranoside; Ino) is a purine ribonucleoside of hypoxanthine, linked to D-ribofuranose through a β-N9-glycosidic bond. In mammalian purine metabolism it is generated by irreversible hydrolytic deamination of adenosine by adenosine deaminase (ADA; EC 3.5.4.4) and cleaved by purine nucleoside phosphorylase (PNP; EC 2.4.2.1) en route to IMP.

A-to-I RNA editing. Inosine is the product of adenosine-to-inosine (A-to-I) RNA editing, one of the most abundant post-transcriptional modifications in the mammalian transcriptome, catalysed by the ADAR family (ADAR1–3) through hydrolytic C6 deamination of adenosines in double-stranded RNA. Because inosine is read as guanosine in reverse transcription and primarily decoded as guanosine in translation, A-to-I editing can recode amino acids, alter splice-site recognition, modulate microRNA biogenesis and targeting, and mark endogenous double-stranded RNA as "self" relative to MDA5-mediated cytosolic dsRNA sensing. It is the analytical target in epitranscriptomic mapping by ICE-seq, Endonuclease V-mediated cleavage and high-resolution LC-MS/MS.

Wobble tRNA decoding. Inosine forms at the wobble position (position 34) of eukaryotic tRNA anticodons, where adenosine is deaminated to inosine by the ADAT2/ADAT3 heterodimer. A single tRNA carrying I34 decodes three synonymous codons (NNU, NNC, NNA), expanding codon-recognition capacity and compressing the tRNA repertoire. The bacterial homologue TadA has been adapted as the deaminase module of adenine base editors (ABEs) for programmable A-to-G genome editing.

Purine salvage and chemoenzymatic synthesis. Inosine is a substrate for purine salvage and a starting material for chemoenzymatic nucleoside synthesis. Mammalian PNP, highly specific for 6-oxopurine nucleosides, catalyses reversible phosphorolysis of inosine to hypoxanthine and α-D-ribose-1-phosphate; hypoxanthine is condensed with PRPP by HGPRT (EC 2.4.2.8) to give IMP, the gateway to AMP and GMP nucleotide pools. This reversibility lets trans-glycosylation through the α-D-ribose-1-phosphate intermediate transfer the sugar to modified purine bases, giving purine nucleoside analogues; pyrimidine analogues require a pyrimidine-specific nucleoside phosphorylase coupled with PNP.

Degenerate oligonucleotide design. Inosine and 2'-deoxyinosine pair with all four canonical bases, making them useful as "wobble positions" in degenerate primer and probe design. In deoxyinosine-containing DNA duplexes pairing stability follows I:C > I:A > I:T ≈ I:G. They reduce the number of oligonucleotides needed to cover sequence variants in consensus primer design across divergent species, conserved-region targeting and probe rescue, but are most useful at positions of true sequence ambiguity, not as a substitute for full specificity.

Analytical and spectroscopic reference. Inosine has a UV absorption maximum near 248–250 nm (ε ≈ 12,000 M⁻¹cm⁻¹ at neutral pH) and a monoisotopic mass of 268.08 Da, and serves as a retention and quantitation standard in reverse-phase and LC-MS analysis of purine nucleosides and nucleotides. Diagnostic ¹H NMR signals include the H1' anomeric proton (δ ≈ 5.9–6.1 ppm, D₂O) and the hypoxanthine H8 and H2 singlets (δ ≈ 8.2–8.3 ppm).

Enzyme-assay reagent. Inosine is a substrate for PNP assays and a product or reference standard in ADA, ADAR and ADAT workflows.

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