title: beta-Carotene quenches singlet oxygen formed by isolated photosystem II reaction centers.
abstract: By measuring time-resolved luminescence emission at 1270 nm, we have detected singlet oxygen formation by illuminated, reaction centers of photosystem II isolated from Pisum sativum, which is in agreement with earlier work (Macpherson, A. N., Telfer, A., Barber, J., & Truscott, T. G. (1993) Biochim. Biophys. Acta 1143, 301-309). In this paper we show that the yield of singlet oxygen is significantly increased if the number of beta-carotene molecules bound per isolated complex is reduced from two to one. We conclude, therefore, that beta-carotene can act as an effective quencher of singlet oxygen in the photosystem II reaction center. This conclusion is supported by the finding that the rate of light-induced irreversible bleaching of chlorins in the reaction center is increased with decreasing beta-carotene levels. The results demonstrate the direct intermediacy of singlet oxygen in causing photooxidative damage within a biological environment and are discussed, specifically, in terms of the role of beta-carotene in protecting photosystem II against photoinhibition.
authors.affiliation: Wolfson Laboratories, Department of Biochemistry, Imperial College of Science, Technology and Medicine, London, U.K.
authors.forename: A
authors.initials: A
authors.lastname: Telfer
authors.forename: S
authors.initials: S
authors.lastname: Dhami
authors.forename: S M
authors.initials: SM
authors.lastname: Bishop
authors.forename: D
authors.initials: D
authors.lastname: Phillips
authors.forename: J
authors.initials: J
authors.lastname: Barber
mesh_terms: D002338:Carotenoids / Q000737:chemistry*; D002474:Cell-Free System; D002734:Chlorophyll / Q000737:chemistry; D066298:In Vitro Techniques; D045342:Light-Harvesting Protein Complexes; D008163:Luminescent Measurements; D010100:Oxygen / Q000737:chemistry*; D010777:Photochemistry; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry*; D045332:Photosystem II Protein Complex; D017382:Reactive Oxygen Species / Q000737:chemistry; D019207:beta Carotene
chemical_list: D045342:Light-Harvesting Protein Complexes; D045322:Photosynthetic Reaction Center Complex Proteins; D045332:Photosystem II Protein Complex; D017382:Reactive Oxygen Species; D019207:beta Carotene; D002734:Chlorophyll; D002338:Carotenoids; D010100:Oxygen