Incorporation of 125I- into membrane proteins from Chlamydomonas (lanes 1, 2), Arabidopsis (lanes 3, 4), and E. coli (lanes 5, 6). CAO was electroeluted from a gel as shown in lane 5 and re-run (lanes 7, 8). Lanes 2, 4, 6 and 8 are radioautograms of Coomassie blue-stained lanes 1, 3, 5 and 7, respectively. Lanes 1 to 6 were from the same gel. A 26 kDa fragment of CAO in lane 6 is labeled with an asterisk. (B), CAO was purified by immunoprecipitation from detergent-solubilized extracts of dark-grown, yellow cells of C. reinhardtii cw15, labeled with 125I-, digested with trypsin and subjected to N-terminal degradation as described in Methods. (C), CAO was purified from light-grown, green cells of C. reinhardtii and treated as under (B). (D), 125I-Labeled CAO from Arabidopsis was analyzed as described in (B). Radioactivity in each fraction was plotted as a percent of the total released in the 20 cycles.