Table 1.

The total number of basic charges for the series of membrane complexes considered here was computed together with the number of basic residues in the transmembrane regions. The most likely location of protonated sites was deduced from the total number of basic residues in the membrane and soluble proteins using MD simulations in vacuum. The number of charges, determined from mass spectra, was assigned to the protonation sites that maintained the most stable structures. The average charge state observed in the electrospray spectrum is also shown.

	total basic residues	basic residues in TM region	charged residues in TM region	average charge state
BtuCD	142	10	0	22.8
CL12	74	0	0	22.2
EmrE	10	1	0	8
Kirbac	184	0	0	25.3
LmrA	116	0	0	18.9
LmrCD	129	2	0	25
MexB	242	18	3	39.9
MtrE	174	3	3	25