Relevant mass shifts reducing the peak overlap are highlighted in the insets. Pictograms illustrate the corresponding complex of detected peaks and asterix highlight heavy isotope-labeled protein as indicated. The different laser intensities are indicated. (a and c) Spectra of labeled and non-labeled samples are shown by a black and a red line, respectively. (a) hHv1-VSD in nanodiscs using MSP1D1ΔH5 scaffold proteins (19.49 kDa). Labeling shifts the hHv1-VSD monomer about 2 kDa. (b) KcsA MSP1E3D1 (DMPG) complexes. Mass shift for the free KcsA tri- and tetramer (3.63 and 4.48 kDa, respectively) are sufficient to stop overlap with other species. (c) Spectra of LspA MSP1D1ΔH5 (DMPC) complexes in black and of LspA MSP1E3D1 (DMPG) complexes in red. 15N, 2H labeled LspA (22.57 kDa) could not be sufficiently separated from MSP1D1ΔH5 (21.46 kDa). However, spectra of unlabeled LspA (21.52 kDa) inserted into MSP1E3D1 discs show no overlap.