Fig. 1.

Schematic representation of the capture, binding, and regeneration cycle. The chip is prepared by cross-linking anti-Fc antibody (AB) on the sensor chip. In the first step of the reaction (1), receptor-Fc fusion protein is captured by the antibody (approximately 150–250 RUs of receptor-Fc fusion protein). In the second step of the reaction (2), 80 nM BMP is injected, and binding to the receptor moiety is detected. In the third step of the reaction (3), the BMP-receptor-Fc fusion complex is eluted with MgCl₂ to regenerate the surface. To test binding of a different BMP, new receptor-Fc fusion protein has to be captured (step 1). A protein A chip can also be used to capture receptor-Fc proteins, but regeneration conditions need to be adapted