Table I. Size and interpretation of the recurring peaks in STEM mass analysis.
| Peak positiona | 1 | 2 | 3 | 4 | 5 |
|---|---|---|---|---|---|
| SecYEG | (SecYEG)2 | (SecYEG)4 | (SecYEG)2 SecA proOmpA | (SecYEG)4 SecA proOmpA | |
| Proteinb | 75 | 150 | 300 | 385 | 535 |
| Micellec | 75 | 100 | 150 | 150 | 150 |
| SecYEG | 176 ± 32 | 268 ± 32 | – | – | – |
| SecYEG after pre-incubation with SecA + AMP–PNP | 183 ± 57 | 289 ± 57 | 421 ± 57 | – | – |
| SecYEG, SecA + ATP, proOmpA | ND | 276 ± 48 | 416 ± 48 | 531 ± 48 | 686 ± 48 |
| Calculatedd | 151 | 287 | 477 | ND | ND |
ND, not determined.
aPeak positions relate to the STEM analysis shown in Figure 7.
bCalculated from the molecular masses in kilodaltons of the indicated proteins.
cThe amount of dodecyl maltoside micelle bound to the purified SecYEG complex was determined to be 100 kDa as described in Materials and methods, and found to be 100 kDa for the SecYEG dimer. The other values are estimates.
dCalculated masses of the SecYEG dimer and tetramer were determined by their surface observed in negative-stain EM after single particle analysis (349 nm2 for the dimer and 582 nm2 for the tetramer), a height of 6 nm, and a density of 1.35 g/cm3, with no correction for the putative pore.