Description APN-Azide is a bifunctional crosslinker for thiol-to-alkyne coupling. This coupling can be performed with high selectivity in biological medium using mild reaction conditions.Standard protein labeling procedure (cysteine labeling)1. Dissolve the protein in the appropriate buffer* with pH 6.5-9.0 (e.g. PBS) at 1-10 mg/mL concentration.2. Apply the appropriate amount of the stock solution of the reagent (1-5 molar eq. per free cysteine residue).3. Incubate at room temperature for 2 hours.4. If necessary, purify the protein-azide conjugate using size exclusion chromatography or ultrafiltration.5. The conjugate can be readily coupled with alkyne-containing using standard click-chemistry protocols.*Note: avoid thiol-containing buffers.