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αO-conotoxin GeXIVA, which is a potent antagonist of α9α10 nicotinic acetylcholine receptor (nAChR), is of great interest as a potential analgesic for chronic neuropathic pain. It has three isomers, of which both GeXIVA[1,2] and GeXIVA[1,4] showed similar low nanomolar IC s in potent blocking rat α9α10 nAChRs. Here, we first reported stabilities of GeXIVA[1,2] and GeXIVA[1,4] in various biochemical circumstances, including human serum, enzymatic degradation, and thiol, which would be the key factors to affect stabilities of the two isomers in vivo. Simultaneously, forced degradation was carried out to evaluate stabilities of the two isomers. GeXIVA[1,2] and GeXIVA[1,4] were unstable when they were incubated in serum and digestive enzymes at 37°C. Their disulfide bond frameworks were easy to be scrambled in GSH and HSA. For different stress conditions, their stabilities were impacted greatly by oxidation, temperature, and alkaline conditions. The results may provide a foundation for storage conditions, structural modification, and pharmaceutical preparation of GeXIVA[1,2] and GeXIVA[1,4].

α‐Conotoxin (CTx) TxID is a potent α3β4 nicotinic acetylcholine receptor (nAChR) antagonist that has been suggested as a potential drug candidate to treat addiction and small cell lung cancer. The function and structure of TxID have been well‐studied, but analyses of its stability have not previously been reported. The purpose of this study was to analyze the stability and forced degradation of TxID under various conditions: acid, alkali, water hydrolysis, oxidation, light, thiols, temperature, ionic strength and buffer pH. Different degradation products were formed under various conditions, and the degradation patterns of TxID showed pseudo‐first‐order kinetics. TxID degraded slowest at pH 3 within a pH range of 2–8. The major degradation products were analyzed using liquid chromatography–tandem mass spectrometry and the activity of the main product with α3β4 nAChR was analyzed using electrophysiological methods. Our analysis of TxID stability may aid the selection of appropriate conditions for peptide production, packaging and storage.

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