Figure 4. Effect of ammonium acetate and detergent concentration on mass spectra of the E. coli ammonium channel, AmtB.

Mass spectra were collected at constant high activation instrument settings. (a) Purified trimeric AmtB channel¹⁷ was buffer exchanged into Mem MS Buffer containing 2× CMC DDM at various concentrations of ammonium acetate. Lower and higher buffer concentrations diminish mass spectra quality. (b) Dilution and addition of DDM to solutions of buffer exchanged AmtB in 200 mM ammonium acetate. Moderate and considerable resolution is lost in 1× and 8× CMC preparations, respectively. At high detergent concentrations, broad peaks are observed corresponding to detergent aggregates, for example in the 2,000 to 4,000 m/z range of the 8× CMC mass spectrum.