negative values

Hi Arnoud,

I am testing a simple interaction between FcG receptors and IgG. There are several receptors that bind IgG, and I am testing 3 of them.
All my receptors bind to IgG immobilised by amine coupling to CM5 chip, however when I flip the format and capture the receptors onto NTA chip (they all have His-tag) then one of them gives me negative values, while the other two are fine.
How can I interpret this?
Many thanks for your help.

Hi,

I have to say that I encountered something similar last month while immobilizing two mutants of the same protein. One had a positive response and one a negative while injecting the same analyte. I tried to get an idea what was happening by injecting the buffer of the analyte but that made no difference.
Sometimes, with amine coupling, we see that high ligand channels give a lower or higher bulk (the expected) when the analyte is injected. But that said, I expect that you have roughly equal amounts captured on the NTA-chip.
Did you try to switch position of the three receptors ruling out some chip position effect? (long shot …. :dry: )

Some other ideas about negative responses you can find at:
www.sprpages.nl/experiments/troubleshooting

Kind regards
Arnoud