SPR analysis of β-glucuronidase binding to immobilized sCD-MPR (A) and E19Q/K137M (B) constructs. sCD-MPR and E19Q/K137M were immobilized on the surface of a CM5 sensor chip to a level of 800 and 770 response units, respectively. β-glucuronidase was injected in a volume of 80 μl over the sensor surface at a rate of 40 μl/min. After 2 min, the solution containing β-glucuronidase was replaced with buffer and the complexes were allowed to dissociate for 2 min. Various concentrations of β-glucuronidase (8, 10, 20, 40, 80, 100, and 120 nM) were injected over the immobilized receptors and the resulting sensorgrams are shown.