Frequently Asked Questions


Please do not hesitate to contact CASLO if you have any questions.

We have collected the following frequently asked questions and the answers:

How do I request a price quotation and order a product?

Answer: Please send your request by e-mail or fill in the contact form. You can also send a fax or telephone us. You will receive a price quotation within 24 hours and in the price quotation are detailed instructions for how to order the product. Prices are inclusive handling and delivery with express courier.

Are there any countries where peptides cannot be delivered?

Answer: CASLO deliver to all countries worldwide. CASLO does however, not deliver products to personal addresses, only to research institutions, universities, companies etc. CASLO only deliver products for research, not for clinical use.

In what format are peptides delivered?

Answer: Peptides are always delivered in lyophilized format. Peptides are as standard delivered as trifluoroacetate (TFA) salts, where positive loaded groups on the peptide are counterbalanced by TFA ions. Peptides can be delivered as chloride or acetate salts, where the peptides are counterbalanced by chloride or acetate ions, there will however, be added an extra charge for change of counterion.

What is the purity of a peptide, and what are the impurities?

Answer: Peptides can be delivered with purities of: >70% up to >99%. Impurities are typically peptides where there are missing one or several amino acids. CASLO can assist you with finding the correct purity for your application.

How do I dissolve a peptide?

Answer: The solubility of a long peptide strongly depends on the hydrophobicity of the peptide's amino acid sequence. A peptide longer than 10 – 15 amino acids is only fully soluble in an aqueous buffer if it has a certain number of hydrophilic amino acids. Hydrophobic peptides can be dissolved in organic solvents like DMSO or similar. A hydrophilic/hydrophobic profile is specified in the certificate of analysis delivered with the peptide together with detailed guidelines for how to dissolve the peptide. If it is necessary, CASLO can predict the solubility and give guidelines for how to dissolve a peptide before it is ordered. If it is predicted that the solubility of a peptide is too low for the planned usage the peptide can be made with a hydrophilic extension at either the N- or C-terminus in order to increase the aqueous solubility. CASLO also offer solubility testing of the peptide, and the solubility will then be written in the certificate.

How should I store a peptide?

Answer: Products shall be stored in lyophilized form in freezer until prior to use. Peptides can be delivered aliquoted in several vials in quantities that are used in each experiment.

What is the shelf life of a peptide?

Answer: Peptides are stable for minimum one year if stored lyophilized in freezer. If peptides are dissolved the shelf life might be reduced. If peptides contain several reactive amino acids that can be oxidized like Trp, Met but especially Cys, the shelf life might also be reduced.

The peptide contains several cysteines and can therefore easily form disulfide bonds. How do I avoid this?

If the peptide sequence contains several cysteines, or other reactive amino acids, which are easily oxidized, CASLO offers to deliver the peptide with small amounts of the reductant DTT. The peptide is only delivered with DTT if this is ordered by the customer.

How shall I measure a peptide concentration?

Answer: The theoretical molar weight (M.W.) and the M.W. detected by mass spectrometry, which are listed in the certificate of analysis delivered together with the peptide, is for the peptide without counterions. In practice however, a peptide is a salt where the positive loadings in the peptide are counterbalanced by counterions. CASLO always deliver detailed instructions for how to calculate the theoretical M.W., including counterions.

Can I use peptides for cell cultures?

Peptides are in general delivered as trifluoroacetate (TFA) salts. Peptide TFA salts can be used for most cell cultures. There are however, some cell cultures that are sensitive to the TFA counterion. For use with these cell cultures CASLO recommend that peptides are delivered as chloride or acetate salts which are natural counterions. Peptides are in general not completely sterile, even though the lyophilization has some sterilization effect. Peptides can be sterile filtrated by standard sterile filters.

How can I make my peptide permeable to cells?

Answer: There are several cell penetrating amino acid sequences, most of them are positively loaded sequences. Peptide synthesis can be prolonged with a cell penetrating sequence. The most commonly used cell penetrating sequence is the HIV-TAT sequence (YGRKKRRQRRR) which is prolonged to the N-terminal part of a peptide. Another way is to conjugate fatty acids to the peptide (for example Myristic acid). The fatty acid will be placed into the fatty acyl core of the phospholipid bilayer of the membrane on eukaryotic cells. They thereby act as a lipid anchor in the biomembrane.

How can I make peptides resistant to degradation in the cells?

Answer: Cells contain several enzymes that degrade peptides and proteins. Peptides can be made more resistant by ordering them with acetylated N-terminus and amidated C-terminus. These modifications are offered without extra charge. Peptides can also be made with D-isomeric form of one or several amino acids in the sequence which also will increase the stability of the peptide.