Fig. 2. Expression and in situ spin labelling of BtuB variants with PaNDA. (A) 10% SDS PAGE of E. coli expressing indicated BtuB mutants. Experimental X-band cw EPR spectra before (black) and after (purple) irradiation of (B) BtuB_F404 → PaNDA and (C) BtuB_F404 (wt) incubated with PaNDA.