Preparation of Fluorescently Labeled Strept avidin

The following sections present suggested protocols for labeling (strept)avidin with selected fluorophores. Other fluorescent probes may be constructed using the reagents and methods discussed in Chapter 9. 

Although FITC and other reactive fluorescein derivatives still are widely used to label (strept)avidin and other proteins, better fluorescence yield and stability will be obtained if one of the newer hydrophilic fluorescein dyes is used. See Chapter 9, Section 1, for additional details on labeling proteins with fluorescein. 

Dissolve (strept)avidin in 0.1M sodium carbonate, pH 9.5, at a concentration of 2-4mg/ml. 

Dissolve FITC in DMF at a concentration of 2mg/ml. Protect from light. 

Add 50-100 pi of the FITC solution to each ml of the (strept)avidin solution. 

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