Carotenoid-binding proteins of photosystem II.
The distribution of the photosynthetic pigments of the chlorophyll-binding proteins or photosystem-II membranes, isolated from dark-adapted maize leaves was determined. Most (80%) of a xanthophyll, violaxanthin, was found in the three minor chlorophyll-a/b proteins CP24, CP26 and CP29 whose function is unknown. Violaxanthin is the precursor of zeaxanthin, which is involved in dissipating excess excitation energy into heat [Demmig-Adams, B. (1991) Biochim. Biophys. Acta 1020, 1-24] under conditions of high transmembrane pH gradient [Gilmore, A. M. & Yamamoto, H. Y. (1992) Proc. Natl Acad. Sci. USA 89, 1899-1903]. We propose that a role for the minor photosystem-II chlorophyll-a/b proteins is the regulation of energy transfer to the reaction centre. It was also confirmed that the photosystem II reaction centre (D1-D2-cytochrome b559) contains beta-carotene as the only carotenoid. However, the two other chlorophyll-a-binding proteins of photosystem II, CP47 and CP43, bind not only beta-carotene, but also the xanthophyll lutein, previously thought to be restricted to chlorophyll-a/b proteins.
Bassi
R
R
Dipartimento di Biologia, Università di Padova, Italy.
Pineau
B
B
Dainese
P
P
Marquardt
J
J
D002338:Carotenoids / Q000378:metabolism*; D002352:Carrier Proteins / Q000302:isolation & purification*; D002499:Centrifugation, Density Gradient; D002734:Chlorophyll / Q000378:metabolism*; D007525:Isoelectric Focusing; D045342:Light-Harvesting Protein Complexes; D045322:Photosynthetic Reaction Center Complex Proteins / Q000032:analysis*; D045332:Photosystem II Protein Complex; D010860:Pigments, Biological / Q000032:analysis; D010940:Plant Proteins / Q000302:isolation & purification
D002352:Carrier Proteins; D045342:Light-Harvesting Protein Complexes; D045322:Photosynthetic Reaction Center Complex Proteins; D045332:Photosystem II Protein Complex; D010860:Pigments, Biological; D010940:Plant Proteins; D002734:Chlorophyll; D002338:Carotenoids