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Note: PTAD-Alkyne must be first activated by stirring in a 1:0.98 molar ratio with 1,3-dibromo-5,5-dimethylhydantoin (product # 157902). Activation is evident upon solution color change from colorless to deep red and the activated reagent should be used immediately.

General Procedure for Protein Modification with PTAD.

Part 1: PTAD activation
Mix together 1:0.98 molar equivalents of unactivated PTAD to 1,3-dibromo-5,5-dimethylhydantoin (product # 157902) in organic solvent (preferred solvents are DMF or acetonitrile; avoid using DMSO)
Color change is observed from colorless/pale yellow to deep red (approximately 5 min of mixing).
After the solution turns red, store the now activated reagent on ice and use for protein modification within 30 min.

Part 2: Protein modification
Add protein solution in mixed phosphate/Tris buffer or Tris buffer (pH should be 6 - 9) to the eppendorf tube (or other vial) containing the activated PTAD reagent prepared above and mix gently at room temperature for up to 30 min. Preferably use 10-fold molar excess of reagent relative to protein. Use protein at a minimum concentration of 1 mg/ml (higher concentrations are preferred for enhanced labeling).
Remove excess unreacted PTAD by gel filtration.

PTAD-Alkyne is a selective bioconjugation reagent for the modification of tyrosine residues with a terminal alkyne. Subsequent modification can then be afforded via the copper catalyzed azide/alkyne click chemistry reaction with an azide containing compound or biomolecule. This reagent has been shown to selectively introduce poly(ethylene glycol) or PEG chains onto proteins with surface exposed tyrosine residues. PTAD-Alkyne has also been used in the formation of antibody-drug conjugates. This reagent is compatible with different buffer systems such as PBS, Tris and mixed PBS/Tris buffer (preferred). The linkage with tyrosine has been shown to be stable to pH and temperature extremes as well as blood plasma.