Sulfo-LC-SPDP

Add 25 pi of the stock solution of either SPDP or LC-SPDP in DMSO to each ml of the protein to be modified. If sulfo-LC-SPDP is used, add 50 pi of the stock solution in water to each ml of protein solution. 

Add 50 pi of the SPDP (or LC-SPDP) solution to the oligo solution. Add 100 pi of the sulfo-LC-SPDP solution, if the water-soluble crosslinker is used. Mix. 

Dissolve SPDP at a concentration of 6.2 mg/ml in DMSO (makes a 20 miVl stock solution). Alternatively, LC-SPDP may be used and dissolved at a concentration of 8.5 mg/ml in DMSO (also makes a 20 mM solution). If the water-soluble Sulfo-LC-SPDP is used, a stock solution in water may be prepared just prior to addition of an aliquot to the thiolation reaction. In this case, prepare a 10 mM solution of Sulfo-LC-SPDP by dissolving 5.2 mg/ml in water. Since an aqueous solution of the cross-linker will degrade by hydrolysis of the sulfo-NHS ester, it should be used quickly to prevent significant loss of activity. If a sufficiently large amount of protein will be modified, the solid may be added directly to the reaction mixture without preparing a stock solution in water to allow accurate weighing of Sulfo-LC-SPDP. 

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