title: Separate photosensitizers mediate degradation of the 32-kDa photosystem II reaction center protein in the visible and UV spectral regions.
abstract: 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.
authors.affiliation: Department of Plant Genetics, Weizmann Institute of Science, Rehovot, Israel.
authors.forename: B M
authors.initials: BM
authors.lastname: Greenberg
authors.forename: V
authors.initials: V
authors.lastname: Gaba
authors.forename: O
authors.initials: O
authors.lastname: Canaani
authors.forename: S
authors.initials: S
authors.lastname: Malkin
authors.forename: A K
authors.initials: AK
authors.lastname: Mattoo
authors.forename: M
authors.initials: M
authors.lastname: Edelman
mesh_terms: D002734:Chlorophyll / Q000378:metabolism* / Q000528:radiation effects; D004307:Dose-Response Relationship, Radiation; D008027:Light; D045342:Light-Harvesting Protein Complexes; D008970:Molecular Weight; D045322:Photosynthetic Reaction Center Complex Proteins; D045332:Photosystem II Protein Complex; D010940:Plant Proteins / Q000378:metabolism* / Q000528:radiation effects; D010944:Plants / Q000378:metabolism* / Q000528:radiation effects; D013472:Sunlight; D014466:Ultraviolet Rays
chemical_list: D045342:Light-Harvesting Protein Complexes; D045322:Photosynthetic Reaction Center Complex Proteins; D045332:Photosystem II Protein Complex; D010940:Plant Proteins; D002734:Chlorophyll