I have just started with SPR to detect interaction between two proteins. I am using CM5 sensor chips for the immobilization of one of my protein (ligand protein)and flowing another analyte protein (Molecular weight 20KD) through the flow channel. I am getting good immobilization of my ligand protein as detected by resonance units and a good enough resonance units obtained during analyte injection to account for interaction.Though the association is good enough to account for binding but the dissociation is not showing as expected.the dissociation curve is not falling after the interaction has happened.Although, I have already checked through in vitro experiments that these two proteins interact with each other. What could be the possible reason for the dissociation curve not falling as it should be?and What should I do next to optimize the interaction between my two proteins using SPR to show an usual and typical dissociation curve?