Interaction with iminobiotin

Figure 11.5 At pH 4, the protonated form of iminobiotin does not interact with the binding sites on avidin or streptavidin. At pH 11, the imino group is unprotonated and regains binding capability toward these proteins.

A second study by this group demonstrated that the specificity of the binding, which is observed in solution, is carried over to the mass spectral analysis (Fig. 12B).39 The active form of strepavidin was reacted with both biotin (Kd 10-15 M) and with iminobiotin (Kd 10-7 M). The data indicated that four molecules of biotin bind to the strepavidin after short incubation times and at low strepavidin-biotin ratios, while under the same conditions, no strepavidin-iminobiotin complexes were observed. This result provided evidence that, for this system, the solution properties (relative binding constants) of the stepavidin-biotin interactions were carried over to the gas phase. 

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