A, SDS-PAGE gel showing overexpression and purification of recombinant pPMSR and cPMSR proteins in E. coli. Lane 1, Non-induced C41 cells; lane 2, C41 cells after 3 h of His-pPMSR induction; lane 3, affinity-purified His-pPMSR; lane 4, purified pPMSR after removal of His tag by thrombin; lane 5, C41 cells after 3 h of His-cPMSR induction; lane 6, affinity-purified His-cPMSR. B, Autoradiograph showing chloroplast import of the Arabidopsis PMSR polypeptide. Lane T, PMSR translation product; lane 1, PMSR translation product incubated with intact pea chloroplasts; lane 2, thermolysin-treated intact chloroplasts after the import incubation; lane 3, stromal fractions after isolation from the thermolysin-treated chloroplasts; and lane 4, thylakoid fractions after isolation from the thermolysin-treated chloroplasts. C, Variation in activity of p-PMSR (○) and c-PMSR (●) at different pH values. Data points are means of duplicate assays performed using N-acetyl-[3H]-MetSO as a substrate.