This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via CrossRef Citing Articles via Google Scholar Google Scholar Articles by Pan, R. S. Articles by Hsu, B. D. Search for Related Content PubMed PubMed Citation Articles by Pan, R. S. Articles by Hsu, B. D. Agricola Articles by Pan, R. S. Articles by Hsu, B. D.

Metabolism and Enzymology

Functional Size of Photosynthetic Electron Transport Chain Determined by Radiation Inactivation ¹

Institute of Radiation Biology, College of Nuclear Sciences, National Tsing Hua University, Hsin Chu 30043, Taiwan, Republic of China

Radiation inactivation technique was employed to determine the functional size of photosynthetic electron transport chain of spinach chloroplasts. The functional size for photosystem I+II (H₂O to methylviologen) was 623 ± 37 kilodaltons; for photosystem II (H₂O to dimethylquinone/ferricyanide), 174 ± 11 kilodaltons; and for photosystem I (reduced diaminodurene to methylviologen), 190 ± 11 kilodaltons. The difference between 364 ± 22 (the sum of 174 ± 11 and 190 ± 11) kilodaltons and 623 ± 37 kilodaltons is partially explained to be due to the presence of two molecules of cytochrome b₆/f complex of 280 kilodaltons. The molecular mass for other partial reactions of photosynthetic electron flow, also measured by radiation inactivation, is reported. The molecular mass obtained by this technique is compared with that determined by other conventional biochemical methods. A working hypothesis for the composition, stoichiometry, and organization of polypeptides for photosynthetic electron transport chain is proposed.