SMPT solubility

SMPT, succinimidyloxycarbonyl-a-methyl-a-(2-pyridyldithio)toluene, contains an NHS ester end and a pyridyl disulfide end similar to SPDP, but its hindered disulfide makes conjugates formed with this reagent more stable (Thorpe et al., 1987) (Chapter 5, Section 1.2). The reagent is especially useful in forming immunotoxin conjugates for in vivo administration (Chapter 21, Section 2.1). A water-soluble analog of this crosslinker containing an extended spacer arm is also commercially available as sulfo-LC-SMPT (Thermo Fisher). 

Since SMPT is not soluble in aqueous solutions it must be first dissolved in organic solvent and an aliquot of this stock solution transferred to the reaction solution. The reagent is soluble... 

Since SMPT is not soluble in aqueous solutions it must be first dissolved in organic... 

Dissolve SMPT (Pierce) at a concentration of 7.7 mg/ml in acetonitrile (makes a 20 mM stock solution). Alternatively, the water-soluble Sulfo-LC-SMPT may be used and dissolved at a concentration of 6 mg/ml in water (makes a 10 mM solution). This should be done just prior to adding an aliquot to the thiolation reaction. 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 to allow accurate weighing of Sulfo-LC-SMPT, the solid may be added directly to the reaction mixture without preparing a stock solution in water. 

A water-soluble analog of SMPT, called sulfo-LC-SMPT or sulfosuccinimidyl-6-... 

Disulfide groups are introduced using one of two heterobifunctional crosslinkers, which can be obtained commercially in water soluble (sulfo) or insoluble form (Pierce) (Fig. 3). We prefer SMPT to SPDP as the pyridyldi-sulfide crosslinker since it generates a molecule with increased stability in vivo because of the protective effect exerted upon the disulfide bond by the methyl group and the benzene ring on the carbon atoms adjacent to the -ss- bond (Fig. 3) (21,22). The procedure used in our laboratory is as follows (23) ... 

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