Transport of Proteins into the Thylakoid Lumen-Stromal Processing and Energy Requirements for the Import of the Precursor to the 23-kDa Protein of PSII

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Transport of the precursor to the 23-kDa protein of photosystem 11 was examined by incubation of the precursor with isolated intact chloroplasts in the presence of ATP in darkness. An intermediary-sized form was accumulated in the stroma at 0.1-1 mM ATP. At higher concentrations of ATP (3.2-10 mM), the precursor was imported into the thylakoid lumen and processed to the mature form. The precursor was not imported even as far as the stroma in the absence of ATP. The intermediary-sized form that accumulated at low concentrations of ATP was imported into the thylakoid lumen and processed to the mature form when chloroplasts were subsequently incubated in the light. These observations indicate that the accumulated intermediary-sized form was suitable for further translocation and that the intermediary-sized form is a transport intermediate that occurs under natural conditions. Import of the protein into the thylakoid lumen, which was observed at the higher concentrations of ATP, was inhibited by the addition of nigericin or carbonylcyanide m-chlorophenyl hydrazine. The effects of these ionophores suggests that the translocation of the protein across thylakoid membrane requires a proton gradient across the membrane. The results together show that the protein is imported from the cytosol into the thylakoid lumen in discrete steps: ATP-driven translocation across envelope membranes, stromal processing to the intermediate, translocation of the intermediate across the thylakoid membrane and final processing to the mature protein within the thylakoids.
日本植物生理学会の論文

Transport of Proteins into the Thylakoid Lumen-Stromal Processing and Energy Requirements for the Import of the Precursor to the 23-kDa Protein of PSII

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