Phosphorylation of the D1 Photosystem II Reaction Center Protein Is Controlled by an Endogenous Circadian Rhythm

A component of the photosystem II reaction center, the 32-kDa protein, is rapidly turned over in the light. The mechanism of its light-dependent metabolism is largely unknown. We quantified the rate of 32-kDa protein degradation over a broad spectral range (UV, visible, and far red). The quantum yield for degradation was highest in the UVB (280-320 nm) region. Spectral evidence demonstrates two distinctly different photosensitizers for 32-kDa protein degradation. The data implicate the bulk photosynthetic pigments (primarily chlorophyll) in the visible and far red regions, and plastoquinone (in one or more of its redox states) in the UV region. A significant portion of 32-kDa protein degradation in sunlight is attributed to UVB irradiance.

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Free Radical Scavengers Inhibit Light-Dependent Degradation of the 32 kDa Photosystem II Reaction Center Protein

Zeitschrift für Naturforschung C ◽

10.1515/znc-1990-0517 ◽

1990 ◽

Vol 45 (5) ◽

pp. 412-417 ◽

Cited By ~ 53

Author(s):

Sudhir K. Sopory ◽

Bruce M. Greenberg ◽

Roshni A. Mehta ◽

Marvin Edelman ◽

Autar K. Mattoo

Keyword(s):

Free Radical ◽

Photosystem Ii ◽

Reaction Center ◽

Electron Flow ◽

Ultra Violet ◽

Causative Factor ◽

Free Radical Scavengers ◽

Radical Scavengers ◽

Free Radical Damage ◽

Reaction Center Protein

Abstract Involvement of oxygen-free radicals in the rapid, light-dependent degradation of the 32 kDa photosystem II reaction center protein was investigated. The free radical scavengers propyl-gallate and uric acid inhibited 32 kDa protein degradation without affecting linear electron flow. The involvement of singlet oxygen was excluded. Protection from degradation was also afforded under ultra-violet and far-red radiations. These data implicate free-radical damage as a common step in the degradation process, and emphasize the oxygen environment as a causative factor in destabilization of the 32 kDa protein.

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[125I]Azido-Ioxynil Labels Val249 of the Photosystem II D -1 Reaction Center Protein

Zeitschrift für Naturforschung C ◽

10.1515/znc-1989-5-617 ◽

1989 ◽

Vol 44 (5-6) ◽

pp. 444-449 ◽

Cited By ~ 17

Author(s):

Walter Oettmeier ◽

Klaus Masson ◽

Jörg Höhfeld

Keyword(s):

Photosystem Ii ◽

Gas Phase ◽

Reaction Center ◽

Specific Binding ◽

Parent Compound ◽

Protein A ◽

Primary Target ◽

Reaction Center Protein ◽

Uv Illumination ◽

Photosystem Ii Particles

Abstract Azido-ioxynil (3,5-diiodo-2-azido-4-hydroxy-benzonitrile) is a potent photosystem II inhibitor (pI50-value 7.38) and as effective as the parent compound ioxynil itself. [125I]azido-ioxynil exhibits specific binding to isolated thylakoids with a binding constant Kb = 7.14. Upon UV -illumination it binds covalently to thylakoids or photosystem II particles. It labels predominantly the 32 kDa D-1 photosystem II reaction center protein . A 41 kDa protein is only tagged in trace amounts. After proteolytic treatment of labeled D -1 protein with Staphylococcus aureaus V8 -protease two major and two minor fragments are obtained. Automated gas phase sequencing of a 7 kDa cleavage peptide revealed that Val249 is the primary target of azido-ioxynil binding. Compared to urea type herbicides, this places the ioxynil binding site in a different environment of the D -1 photosystem II protein.

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