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How pure are Discovery® Peptides?
Unless otherwise specified, the HPLC purity of our peptides is greater than 95%. Most peptides are analysed by Reverse-Phase HPLC using C18 functionalised silica and all are characterised by MALDI-TOF or LC-MS. Peptides containing N-terminal glutamine (Gln), residues prone to oxidation such as cysteine (Cys), methionine (Met) and tryptophan (Trp), or labile bonds are prone to degradation and may be of lower purity.
How do I know how much ‘real’ peptide is in my peptide solid?
The quantity of peptide stated on the label corresponds to the gross weight. Part of the weight is made up of water and trifluoroacetate counter-ions (unless otherwise stated). Trifluoroacetic acid (TFA) is present in the mobile phases used for purification of the peptide and binds to basic residues such as arginine (Arg), lysine (Lys), histidine (His) or the free N-terminus of the peptide. The peptide content or net peptide amount is typically around 70-80% of the gross weight. Net Peptide content is also determined for each Discovery® peptide batch.
How do I dissolve my peptide?
Peptide containing basic residues (Arg, Lys, His) tend to be fairly soluble in water. Peptides with a majority of acidic residues (Asp, Glu) solubilise better when the pH is increased however this is not desirable when Cys residues are present. Peptides with a large proportion of hydrophobic residues (Ala, Ile, Val, Leu, Phe, Met, Trp) tend to be poorly soluble in water and can be solubilised in organic solvents such as DMSO, formic acid or acetic acid. The organic content can then be reduced by dilution to the desired concentration. DMSO should be avoided with Cys containing peptides.
How should I look after and store my peptide?
Long-term, peptides are best stored as lyophilised powder at -20°C. Short-term storage at 4°C in a refrigerator is acceptable in most cases. Residues such as Cys, Met, Trp, Asn, Gln are prone to mid-to long-term degradation (oxidation, hydrolysis for instance). Peptides may be aliquoted in a degassed buffer or a dry organic solvent and stored frozen but freeze-thaw cycles should be avoided. Peptides labelled with fluorophores should be kept in the dark.
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