(a) SDS–PAGE analysis of AtDJ-1D at different steps of the purification process. Lane 1, marker (labelled in kDa); lane 2, total cell lysate; lane 3, supernatant after cell lysis; lane 4, pellet after cell lysis; lane 5, proteins from an Ni–NTA affinity column; lane 6, proteins separated after anion-exchange chromatography; lane 7, proteins separated after Superdex 200 chromatography (8.5 µg protein used). (b) Superdex 200 size-exclusion chromatography of AtDJ-1D. A single peak corresponding to a monomer was observed. The scale at the bottom indicates the elution volume. Inset, semi log plot of the molecular mass of the standard proteins used versus their logKd values.