FIGURE 6.
Mass spectra of His-tagged NeuTTM in the absence of added substrates and divalent cations. M, monomer (theoretical mass = 19,987.4 Da); M2, dimer (theoretical mass = 39,974.8 Da). A, shown is a spectrum recorded in harsher source conditions (RF lens 1 voltage = 150 V); the dimer was partially destroyed, but the mass accuracy was higher. B, shown is a spectrum recorded in soft source conditions (RF lens 1 voltage = 50 V), showing that the dimer is the most abundant species in solution. The protein concentration was 10 μm in 100 mm ammonium acetate, pH 6.5.