Table 2.
Intact Protein Mass Spectrometry of the F. diplosiphon SF33 Cyt b6f Complex after Ni Affinity Chromatography
| retention time (min) | measured average molecular mass (Da) | calculated average molecular mass (Da) | measured monoisotopic molecular mass (Da) | modifications | subunit identity |
|---|---|---|---|---|---|
| 35.7 | 14578.1 | 14579.3917 | 14567.0896 | 42–179 | ISP (truncated) |
| 46.1 | 18939.5 | 18940.3345 | NA | 2–179, N-acetyl | ISP (full length) |
| 50.9 | 32743.0 | 32718.4635 | NA | 36–333 + six His, heme | cyt f (PetA)a |
| 53.4 | 31768.0 | 31748.4403 | NA | 36–332, heme | cyt f (without N333, His tag) |
| 84.0 | 4026.1 | 4025.7869 | 4023.1578 | N-formyl | PetG |
| 95.9 | 3578.0 | 3578.2265b | 3575.8351 | N-formyl | PetMc |
| 97.8 | 3254.6 | 3256.0387d | 3252.8471 | N-formyl | PetLd |
| 100 | 24772.6 | 24771.6082 | NA | N-acetyl, heme | cyt b6 (PetB) |
| 109 | 3261.5 | 3261.9616 | 3259.7588 | N-formyl | PetN |
| 110 | 17409.3 | 17409.7298 | NA | Met1 removed | PetD |
During the course of this analysis, the results presented in our 2002 paper were reviewed. The current spinach PetA sequence (P16013; September, 6, 2014) now yields full mass match with the same modifications we originally reported, further supporting the YP motif at the N-terminus of this protein.
Based upon the PetM sequence of N. azollae (strain 0708) (D7DYS4).
BLAST searches of a pair of sequence tags (FGLIFV and GALLLK) match various cyanobacterial PetM sequences from the Nostocales. D7DYS4 provided a full sequence in agreement with the low- and high-resolution mass spectrometry data.
Based upon the PetL sequence of N. azollae (strain 0708) (D7E059).