Radiolabelled Peptides

Cambridge Research Biochemicals (CRB) is the second oldest custom manufacturer of peptides in the world, with 30 years of experience of providing high quality bespoke peptides.

Strategic Alliances

CRB is able to leverage this expertise in peptide synthesis, through unique collaborations with major radio-synthesis groups, to provide peptides and proteins labelled with tritium (³H), carbon-14 (¹⁴C) and iodine-125 (¹²⁵I).

Features of Radiolabelling Service

• Product shipped directly from the radiochemical laboratory to the customer
• CRB liaises with shipping broker to ensure smooth and problem free delivery to the customer
• Trititated Peptides are usually supplied in 10% aqueous ethanol to improve stability
• Cold reference peptide is made as standard to determine specific activity. Cold peptide can be used as diluent to improve stability of hot peptide
• Small organic molecules can also be prepared radiolabelled
• Custom aliquotting upon request

Pure specifically tritiated peptides can be made for use in receptor studies, metabolic studies and pharmacological investigation.

Tritium reduction by catalytic exchange is the simplest and most economic route for labelling peptides that do not contain Cysteine residues.

Analogues of the peptide containing one or more of Phe, Pro, Tyr, or Leu residues substituted with a double bond or halogen moiety are synthesised at CRB and sent to the radio-synthesis group where these precursor peptides are then reduced with Tritium to generate the desired tritium labelled peptide with a specific activity in the range of 10-100Ci/mmole.

Iodine-125 (¹²⁵I) labelled Peptides and proteins

Iodine-125, with a half-life of 60 days, is a cost-effective choice for labelling of peptides and proteins, as the reaction is performed directly on the peptide or protein sample. CRB offers a fixed fee service for iodination (2 x 50 mCi[¹²⁵I]) and HPLC purification. For peptides and proteins containing tyrosine residues, iodination is carried out with Na¹²⁵I activated with chloramin-T, lactoperoxidase or iodogen. Alternatively, free amino functions of the protein can be labelled using ¹²⁵I-Bolton-Hunter reagent.

Carbon-14 (¹⁴C) labelled Peptides

Carbon-14 should only be considered after Tritium for two reasons: Carbon-14 can only be incorporated in to peptides via an expensive Carbon-14 labelled amino acid or by addition to the N-terminus of the peptide (e.g. ¹⁴C-Acetic acid to form ¹⁴C-Acetyl-peptide) and secondly due to the thousand-fold reduction in specific activity.

Tritium labelling

The simplest route to tritium labelled peptides involves the catalytic hydrogenation or hydrogenolysis of a peptide analogue containing unsaturated or iodinated precursor amino acid derivatives (Figure 1). These peptides are assembled, purified and characterised in the same way as other peptides and then treated with tritium gas to generate the tritium labelled peptide.

¹²⁵I labelling

Labelling with iodine-125 normally involves incorporation of iodine-125 into tyrosine or histidine residues within the peptide or protein (Figure 2). This is done by treatment of the sample with Na¹²⁵I in the presence of an oxidising reagent to generate a source of electrophilic iodine. Usually, one or two iodine atoms are added depending on conditions used. For peptides and proteins lacking accessible tyrosine residues, free amines can be derivatised with Bolton-Hunter reagent prior to iodination.

¹⁴C labelling

The simplest approach to ¹⁴C labelling involves acetylation of free amino groups in the peptide with ¹⁴C-acetic acid to provide peptides with a specific activity of up to 120mCi/mmol. Glycine also can be prepared with one or both carbon atoms labelled with carbon-14 leading to a maximum specific activity of 100-120mCi/mmole and incorporated during peptide assembly.

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Get in touch

Tel: +44 (0) 1642 567 180
Fax: +44 (0) 1642 567 181
Email: crbsales@crbdiscovery.com