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Titration with 3‐(3,4‐dichlorophenyl)‐1,1‐dimethylurea (DCMU) as Evidence for Several Photophosphorylation Sites in Scenedesmus
Author(s) -
KYLIN A.,
SUNDBERG I.,
TILLBERG J.E.
Publication year - 1972
Publication title -
physiologia plantarum
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.351
H-Index - 146
eISSN - 1399-3054
pISSN - 0031-9317
DOI - 10.1111/j.1399-3054.1972.tb03631.x
Subject(s) - dcmu , photophosphorylation , chemistry , hill reaction , biochemistry , photosynthesis , photosystem ii , chloroplast , gene
Photophosphorylation was measured in intact cells of Scenedesmus obtusiusculus , which were made phosphate starved before the start of the experiments. Photophosphorylation was titrated with narrow intervals of 3‐(3,4‐dichlorophenyl)‐1,1‐dimethylurea (DCMU) from 10 ‐7 M upwards. Plots of the reciprocal of photophosphorylation against concentration of DCMU gives three essentially straight lines; one between 10 ‐7 and 10 ‐6 M DCMU; one between 10 ‐6 and 6 · 10 ‐6 M DCMU; and one for more than 6 · 10 ‐6 M DCMU, the last‐mentioned line being parallel to the abscissa. The stoichiometry between the three reactions is roughly 2: 1: 1. At least three sites for photophosphorylation are indicated, and the assumption that all sites work with approximately the same efficiency would make them four.