Orexin B Reference
Reviewed by Dr. Martina Rossi, PhD
Scientific Contributor and Reviewer · Reviewed
Molecular Profile
Compound
Orexin B
Also known as
Hypocretin-2
CAS number
205640-91-1
Molecular formula
C123H212N44O35S
Molecular weight
2899.30 g/mol
Amino acid sequence
RSGPPGLQGRLQRLLQASGNHAAGILTM-NH2
Purity
greater than 99 percent
Physical form
Lyophilized powder
What Orexin B is, structurally
Orexin B is a peptide of twenty-eight residues, and the product page describes it as linear, in explicit contrast with Orexin A, which is folded and holds two disulfide bridges. That contrast is the most useful thing to know about handling this compound, because almost everything that dominates the other peptide's care is simply absent here.
The formula supports the description. There is one sulfur, and one sulfur cannot form an intramolecular disulfide, which requires two. The deposited structure for this CAS settles what that single atom is: it shows a methionine thioether, with no disulfide bond and no free thiol anywhere in the molecule.
That single fact removes a great deal. There is no cross-link to reduce, so reducing agents are not the hazard they are on the folded peptide. There is no scrambling risk, so the isomeric failure that a mass check cannot detect does not arise. There is no free thiol, so no oxidative dimerisation. What remains is the ordinary methionine liability: oxidation to the sulfoxide, adding sixteen units.
The composition is the other half of the picture, and it runs opposite to most peptides of this length. Of forty-four nitrogens, twenty-eight are on the backbone, twenty-seven amides plus the free N-terminal amine, and one is the C-terminal amide, leaving fifteen on side chains. Of thirty-five oxygens, twenty-eight or twenty-nine belong to the backbone, leaving only six or seven. The composition is strongly basic for a different reason than the raw counts: three arginines and one histidine sit against no acidic side chain anywhere, and the C-terminus is amidated rather than free. Nine of the fifteen side-chain nitrogens are arginine guanidinium and two are histidine, while the remaining four belong to glutamine and asparagine amides and are not basic.
That inverts the usual dissolution advice in a way worth being deliberate about. A basic peptide carries net positive charge at neutral pH and has a high isoelectric point, so lowering the pH increases its charge and its solubility. Where an acidic peptide is driven toward precipitation by a drop of dilute acetic acid, this one is helped by it.
Structure at a glance
NH2: C-terminal amide. Letters are one-letter amino acid codes.
Drawn from the product database.
Reconstitution and handling
Sterile water is the default solvent. Where a vial dissolves reluctantly, mildly acidic conditions are the right escalation here rather than the wrong one, for the reason above, and dilute acetic acid is the conventional choice.
Add diluent slowly down the inside wall of the vial, swirl gently, and let the solution clarify. Do not vortex; it introduces foam without dissolving anything faster.
No reducing agent is needed, since there is no disulfide for one to act on.
Adsorption deserves attention on a basic peptide. A net positive molecule binds readily to borosilicate glass, whose surface is negatively charged, so glass is a poorer choice here and low-protein-binding polypropylene the better default.
This is laboratory preparation chemistry, not dosing, administration, or protocol guidance of any kind.
Storage and stability
Store the lyophilized powder at -20 degrees C, sealed, desiccated and protected from light, and let a cold vial warm before opening. Reconstituted, hold at 2 to 8 degrees C, or aliquot and freeze rather than thawing repeatedly. A linear peptide has no fold to lose, so freeze-thaw is less damaging here than on the folded counterpart, though it remains worth limiting.
Methionine oxidation is the named liability. Air exposure, warmth and light all accelerate it, and the product is sixteen units heavier, which mass spectrometry resolves cleanly at this size. A sealed, cold, dark vial is the control.
The low side-chain oxygen count means comparatively few acidic and hydroxyl residues, which limits though does not eliminate the hydrolytic routes. The stated sequence names them: three glutamines and an asparagine are the deamidation candidates, and no aspartate appears, so isomerization does not arise.
These are storage conditions for the material, not dosing or administration guidance.
How Orexin B is tested
Reversed-phase HPLC establishes chromatographic purity as area percent. A basic, highly charged peptide retains weakly on a standard C18 column, so high-aqueous starting conditions or an ion-pairing mobile phase should be expected, and trifluoroacetic acid in the mobile phase serves that purpose as well as improving peak shape.
Area percent is a chromatographic measure and not peptide content by weight. Solid-phase synthesis delivers a salt, and on a strongly basic peptide the counter-ion is a substantial proportional share of the vial contents.
Mass spectrometry confirms identity against 2899.30. A result sixteen units high indicates the methionine sulfoxide. Unlike the folded counterpart, there is no disulfide state to establish and no reduced-versus-oxidized comparison to run, so the identity check here is the straightforward one.
These describe general methodology, not a claim about any particular batch.
Handling FAQ
Is this the same compound as Orexin A?+−
No. They are separate products. Orexin A is thirty-three residues, folded, with two internal disulfide bridges; this is twenty-eight residues and linear. The masses differ by well over six hundred units, so the two are not readily confused on analysis.
The vial is slow to dissolve. Does adding acid help?+−
Here, yes. The composition is strongly basic, so the isoelectric point is high and lowering the pH increases net charge and solubility. This is the opposite of the correct answer for an acidic peptide, where acid drives the solution toward minimum solubility. Full specifications for Orexin B.
Reviewed for scientific accuracy
Dr. Martina Rossi, PhD
PhD, Université Grenoble Alpes · Scientific Contributor and Reviewer
Dr. Rossi's doctoral research at Université Grenoble Alpes examined the vascular functions of bone morphogenetic proteins. Her peer-reviewed work spans cell and molecular biology, vascular biology, and gene therapy, in journals including Cardiovascular Research, Scientific Reports, and Brain Sciences. She reviews Pure Peptides' product, reference, and research pages for scientific accuracy against the sources they cite.
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