FIGURE 2.

Titration of IαI with sulfo-NHS-acetate. IαI was titrated with increasing amounts of the primary amine blocking agent sulfo-NHS-acetate (molar ratios from 1:65 to 1:2100). The reaction was quenched with 150 mm Tris-HCl after 60 min and the samples were analyzed by native-PAGE. When Lys residues are blocked with sulfo-NHS-acetate, the migration of IαI into the gel is reduced and IαI appears as a less compact protein. IαI (lane 1) and IαI cross-linked with BS3 (lane 8) controls were included. This migration is similar to the migration seen when IαI is cross-linked with BS3. The data represent 3 independent experiments.