Abstract
A photosystem I reaction center was isolated from Chlamydomonas reinhardii chloroplasts. It consists of four different polypeptides with Mr approximately 70,000 (subunit I), 19,000 (subunit II), 10,000 (subunit III), and 8,000 (subunit IV). In the presence of salts, the purified reaction center was active in cytochrome 552 photooxidation. Short term labeling experiments with [35S]sulfate revealed that subunit III contains no cysteine or methionine. Subunits I and IV were shown to be chloroplast translation products, while subunit II appears to be synthesized on cytoplasmic ribosomes. The site of synthesis of the subunits to the proton-ATPase complex was studied. A differential effect of cycloheximide on the assembly of photosystem I reaction center and the proton-ATPase complex was indicated.
Highlights
Chlorophyll/ml were harvested by centrifugation at 1500 X g for 3 min and washed twice with growth medium in which the MgSO, was replaced by an equal weight of MgC12
The suspenfour equal parts and protein synthesis sively used in geneticand biogenesis studies of photosynthesis inhibitors
We report on the purification of the photo- containing 0.4 M sucrose, 0.01 M NaC1, and 0.01 M Tricinesystem I reaction center from Chlamydomonas chloroplasts
Summary
From the Departmentof Biology, Technion-Israel Instituteof Technology, Haifa, Israel. A photosystem I reaction center was isolated from [”%]Sulfate was obtained from the Nuclear Research Centre, Negev, Chlamydomonas reinhardii chloroplasts. Thesis of the subunits to the proton-ATPase complex Growing and Labeling of Cells-Chlamydomonas reinhardii was studied. A differential effect of cycloheximide on (strain Y-1) was grownas previously described [17].For labeling with the assemblyof photosystem I reaction center and the [35S]sulfate,-6 liters of cell suspension containing 10 to 20pgof proton-ATPase complexwas indicated. The presence of polypeptides of cytoplasmic and chloroplastic origin in partially purified preparations of photosystems I and I1 was indicated [6]. A photosystem I reaction center was isolated from higher to 10% of that in the original growth medium. The cells were harvested, washed, and broken as described above and under “Results.”
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