Abstract
Dibromothymoquinone (2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone) is reputed to be a plastoquinone antagonist which prevents the photoreduction of hydrophilic oxidants such as ferredoxin-NADP+. However, we have found that dibromothymoquinone inhibits only a small part of the photoreduction of lipophilic oxidants such as oxidized p-phenylenediamine. Dibromothymoquinone-resistant photoreduction reactions are coupled to phosphorylation, about 0.4 molecules of ATP consistently being formed for every pair of electrons transported. Dibromothymoquinone itself is a lipophilic oxidant which can be photoreduced by chloroplasts, then reoxidized by ferricyanide or oxygen. The electron transport thus catalysed also supports phosphorylation and the P e2 ratio is again 0.4. It is concluded that there is a site of phosphorylation before the dibromothymoquinone block and another site of phosphorylation after the block. The former site must be associated with electron transfer reactions near Photosystem II, while the latter site is presumably associated with the transfer of electrons from plastoquinone to cytochrome f.
| Original language | English (US) |
|---|---|
| Pages (from-to) | 119-128 |
| Number of pages | 10 |
| Journal | BBA - Bioenergetics |
| Volume | 305 |
| Issue number | 1 |
| DOIs | |
| State | Published - Apr 27 1973 |
| Externally published | Yes |
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ASJC Scopus subject areas
- Biophysics
- Biochemistry
- Cell Biology
Cite this
Electron transport and photophosphorylation in chloroplasts as a function of the electron acceptor. III. A dibromothymoquinone-insensitive phosphorylation reaction associated with Photosystem II. / Izawa, S.; Gould, J. Michael; Ort, Donald R.; Felker, P.; Good, N. E.
In: BBA - Bioenergetics, Vol. 305, No. 1, 27.04.1973, p. 119-128.Research output: Contribution to journal › Article
}
TY - JOUR
T1 - Electron transport and photophosphorylation in chloroplasts as a function of the electron acceptor. III. A dibromothymoquinone-insensitive phosphorylation reaction associated with Photosystem II
AU - Izawa, S.
AU - Gould, J. Michael
AU - Ort, Donald R.
AU - Felker, P.
AU - Good, N. E.
PY - 1973/4/27
Y1 - 1973/4/27
N2 - Dibromothymoquinone (2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone) is reputed to be a plastoquinone antagonist which prevents the photoreduction of hydrophilic oxidants such as ferredoxin-NADP+. However, we have found that dibromothymoquinone inhibits only a small part of the photoreduction of lipophilic oxidants such as oxidized p-phenylenediamine. Dibromothymoquinone-resistant photoreduction reactions are coupled to phosphorylation, about 0.4 molecules of ATP consistently being formed for every pair of electrons transported. Dibromothymoquinone itself is a lipophilic oxidant which can be photoreduced by chloroplasts, then reoxidized by ferricyanide or oxygen. The electron transport thus catalysed also supports phosphorylation and the P e2 ratio is again 0.4. It is concluded that there is a site of phosphorylation before the dibromothymoquinone block and another site of phosphorylation after the block. The former site must be associated with electron transfer reactions near Photosystem II, while the latter site is presumably associated with the transfer of electrons from plastoquinone to cytochrome f.
AB - Dibromothymoquinone (2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone) is reputed to be a plastoquinone antagonist which prevents the photoreduction of hydrophilic oxidants such as ferredoxin-NADP+. However, we have found that dibromothymoquinone inhibits only a small part of the photoreduction of lipophilic oxidants such as oxidized p-phenylenediamine. Dibromothymoquinone-resistant photoreduction reactions are coupled to phosphorylation, about 0.4 molecules of ATP consistently being formed for every pair of electrons transported. Dibromothymoquinone itself is a lipophilic oxidant which can be photoreduced by chloroplasts, then reoxidized by ferricyanide or oxygen. The electron transport thus catalysed also supports phosphorylation and the P e2 ratio is again 0.4. It is concluded that there is a site of phosphorylation before the dibromothymoquinone block and another site of phosphorylation after the block. The former site must be associated with electron transfer reactions near Photosystem II, while the latter site is presumably associated with the transfer of electrons from plastoquinone to cytochrome f.
UR - http://www.scopus.com/inward/record.url?scp=0015937224&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=0015937224&partnerID=8YFLogxK
U2 - 10.1016/0005-2728(73)90237-5
DO - 10.1016/0005-2728(73)90237-5
M3 - Article
C2 - 4719595
AN - SCOPUS:0015937224
VL - 305
SP - 119
EP - 128
JO - Biochimica et Biophysica Acta - Bioenergetics
JF - Biochimica et Biophysica Acta - Bioenergetics
SN - 0005-2728
IS - 1
ER -