PEG Modification Reagents

Dissolve the biotin-PEG -amine reagent in reaction buffer at a concentration of 25 mM. 

Add a quantity of the biotin-PEG -amine solution to the solution containing the car-boxylate molecule to achieve the desired molar excess. For molecules containing a single carboxylate to be modified, a 1.5- to 2-fold molar excess may be sufficient. However, for proteins or peptides that also contain competing amines, a much larger excess of biotin compound should be used (e.g., 100-fold excess). For instance, for protein biotinylation, add 120 pi of the biotin-PEG -amine solution per ml of the solution prepared in Step 1. 

Immediately before use, dissolve EDC in reaction buffer at a concentration of 25 mM. Add 12 pi of this solution per ml of the combined solution from Step 2. Mix well. 

React for 2 hours at room temperature or 4 hours at 4°C with gentle mixing. 

Purify the biotinylated protein or molecule using dialysis or gel filtration. For small molecule biotinylation where these separation methods may not be appropriate, other procedures may have to be developed, such as reverse-phase chromatography or organic precipitation techniques. 

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