Structural Changes in D1/D2/Cytochrome b₅₅₉ Complex of the Reaction Center of Photosystem II Induced by Short Wavelength UV Irradiation

O. V. Nikitishena,^1,2 M. S. Khristin,¹ T. N. Smolova,¹ and V. V. Klimov¹

¹Institute of Soil Science and Photosynthesis, Russian Academy of Sciences, Pushchino, Moscow Region, 142292 Russia; fax: (27) 79-0532; E-mail: sotnikov@issp.serpukhov.su

²To whom correspondence should be addressed.

Submitted April 21, 1997; revision submitted June 16, 1997.

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Isolated D1/D2/cytochrome b₅₅₉ of photosystem II (PS II) was separated into two chlorophyll--protein bands by isoelectrofocusing in a polyacrylamide gel after irradiation with short-wavelength UV light (UVL) (250-270 nm) which did not depend on the presence of O₂. One of these bands corresponds to the native D1/D2/cytochrome b₅₅₉ complex, whereas the other corresponds to a modified complex which differs from the former in pI, absorption spectrum, and polypeptide composition. The modified complex comprises fragments of D1 and D2 proteins. Fragments with molecular weight 26, 20, 14, 11, and 7 kD were detected after irradiation under aerobic conditions, and fragments with molecular weights 26 and 14 kD were detected after irradiation under anaerobic conditions. Quantitative analysis of pigments demonstrated that the short wavelength UVL absorbed by the proteins induce the photobleaching of all the pigments of isolated RC: chlorophyll a, pheophytin a, and beta-carotene. beta-Carotene is the pigment most sensitive to UVL irradiation. It is thought that short wavelength UVL induces photosensitized bleaching of the pigments.

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KEY WORDS: photosystem II, pigment--protein complex, reaction center, photoinactivation.

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