title: Photoinhibition of manganese enzymes: insights into the mechanism of photosystem II photoinhibition.
abstract: Evidence has recently been presented that photoinhibition of photosystem II (PSII) is triggered by absorption of light by the oxygen-evolving manganese cluster. To get insight into the effects of light on enzymes containing manganese or other transition metal cofactors, the photosensitivities of Mn catalase, Mn superoxide dismutase, the haem (Fe)-containing bovine liver catalase, and CuZn superoxide dismutase were investigated. Glucose oxidase was studied as an example of an enzyme that does not have a metal cofactor. Sensitivities of these five enzymes to UVC, UVA, and visible light were compared in anaerobic conditions. The Mn(III)-oxo-Mn(III)-containing Mn catalase was found to be more sensitive to both visible and UV light than bovine liver catalase. Furthermore, the action spectrum of photoinhibition of Mn catalase was found to be fairly similar to that of photoinhibition of PSII. The Mn(II)-containing Mn superoxide dismutase was sensitive to UVC light and somewhat sensitive to UVA light, while only UVC light caused some inhibition of CuZn superoxide dismutase. Glucose oxidase was the least photosensitive of the enzymes studied. The photosensitivity of Mn enzymes supports the hypothesis that the oxygen-evolving manganese complex of PSII can be damaged by UV and visible light absorbed by its Mn(III) or Mn(IV) ions.
authors.affiliation: Department of Plant Physiology and Molecular Biology, University of Turku, 20014 University of Turku, Finland.
authors.forename: Marja
authors.initials: M
authors.lastname: Hakala
authors.forename: Susanne
authors.initials: S
authors.lastname: Rantamäki
authors.forename: Eeva-Maija
authors.initials: EM
authors.lastname: Puputti
authors.forename: Taina
authors.initials: T
authors.lastname: Tyystjärvi
authors.forename: Esa
authors.initials: E
authors.lastname: Tyystjärvi
mesh_terms: D002374:Catalase / Q000528:radiation effects*; D005949:Glucose Oxidase / Q000528:radiation effects; D008027:Light / Q000009:adverse effects; D008345:Manganese / Q000378:metabolism; D010100:Oxygen / Q000378:metabolism; D045332:Photosystem II Protein Complex / Q000528:radiation effects*; D010944:Plants / Q000201:enzymology* / Q000528:radiation effects*; D013053:Spectrophotometry; D013482:Superoxide Dismutase / Q000528:radiation effects*; D014466:Ultraviolet Rays / Q000009:adverse effects
chemical_list: D045332:Photosystem II Protein Complex; D008345:Manganese; D005949:Glucose Oxidase; D002374:Catalase; D013482:Superoxide Dismutase; D010100:Oxygen