Table 1.
High resolution mass spectrometry
| Peak identification | Experimental mass | Assingment | Theoretical mass |
|---|---|---|---|
| A | 71 370 | A − met | 71369.9 |
| A′ | 71 506 | Intact A | 71501.1 |
| A* | 71 770 | A − met + SAM | 71768.3 |
| A*′ | 71 903 | Intact A + SAM | 71899.5 |
| AB | 110 543 | (A − met)B | 110530.7 |
| A′B | 110 664 | (Intact A)B | 110661.9 |
| A*B | 110 937 | (A − met + SAM)B | 110929.1 |
| A*′B | 111 053 | (Intact A + SAM)B | 111060.3 |
A, A′, A* and A*′ denote the four peaks from the +17 state of the A protein shown in Figure 2. AB, A′B, A*B and A*′B specify the equivalent peaks from the +21 state of the AB heterodimer protein (not shown; theoretical mass of B subunit: 39160.8 Da). Experimental masses for each peak were evaluated as before (11) and the forms of the BcgI protein that best match each experimental mass is recorded along with its theoretical mass; ‘A − met’ notes the protein lacking its N-terminal methionine and ‘Intact A’ the protein starting with the methionine.