(B) Co-elution of periplasmic glucan and radiolabellediron-glucan complex. Periplasmic glucan was isolated from the 55Fe2+-loaded cells, and analyzed by BioGel-P4 size-exclusion chromatography. Fractions (1.5 ml) were collected at a flow rate of 20 ml/h and assayed for glucan using the phenol-sulphuric acid colorimetric assay, and radioactivity was measured to detect the presence of 55Fe. 