Quaternary structure regulation of Rap2.4a under oxidizing and reducing conditions. (A) RAP2.4a was incubated in the presence of DTT and H2O2 before separation on 12% SDS-PAGE and Western blot analysis using anti-HIS antibody. Rap2.4a oligomers monomerized with increasing DTT concentration. Oxidation by H2O2 resulted in oligomeric complexes with low transfer efficiency. From a series with gradually increasing DTT and H2O2 concentrations, the key steps are presented. Monomeric Rap2.4a was detected after reduction with β-mercaptoethanol. (B) Redox titration of Rap2.4a. The quaternary structure of heterologously expressed His-tagged Rap2.4a was analysed relative to the redox poise of the medium by SDS-PAGE separation, Western blotting and detection with anti-His antibody. The band intensities were quantified using the GelScan software package (BIOSCITECH, Marburg, Germany). The redox potential of Rap2.4a was determined from the value at which the complex was 50% dissociated.