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B., Ed.) pp 288-300, Wiley, London. Tinoco, I., Jr. (1962) Adv. Chem. Phys. 4, 113-160. Van Metter, R. L. (1977) Biochim. Biophys. Acta 462, tamante, C. (1986) J. Chem. Phys. 84, 1916-1921. Vol. 1, pp 293-330, Academic, New York. 3454-3458. 1627-1 638. 325-33 1. 538-542. Vol. 111, pp 225-248, Academic, New York. 642-6 5 4. Reversible Changes in Macroorganization of the Light-Harvesting Chlorophyll a/b Pigment-Protein Complex Detected by Circular Dichroism? Gyozo Garab,f Richard C. Leegood,$ David A. Walker,§ John C. Sutherland, and Geoffrey Hind* Biology Department, Brookhaven National Laboratory, Upton, New York 11 973 Received July 9, 1987; Revised Manuscript Received December 3, 1987 ABSTRACT: Light-induced changes in circular dichroism (CD) were studied in thylakoids isolated from spinach. The following features of CD responses occurring in the time range of 10 s to 1-3 min were noted: (i) The kinetics and relative amplitudes of the responses are similar over broad spectral ranges surrounding the major CD bands, i.e., between 670 and 760 nm and between 480 and 550 nm. This applies not only to randomly oriented samples but also to magnetically aligned membranes having markedly different CD spectra in the dark. (ii) Photosystem I is much more effective than photosystem zyxwv I1 and can drive a 40-8096 decrease in CD signal relative to the dark control level. (iii) Photosystem I driven changes are fully inhibited by nigericin or NH4Cl but are largely insensitive to gramicidin. CD changes driven by photosystem 11, on the other hand, are sensitive to all of these reagents. (iv) The CD responses can be shown to originate in circular differential scattering rather than in circular differential absorbance. They can also be distinguished from light-induced, nonpolarized scattering changes. The data are qualitatively evaluated with respect to the theory of circular differential scattering of large helically organized macroaggregates, the size of which is commensurate with the wavelength of the measuring beam [Bustamante, C., Maestre, M. F., & Keller, D. (1985) Biopolymers 24, 1595-16121. The observed decrease of the large CD signal is ascribed to a partial loss of macrohelicity in the light-harvesting chlorophyll a/b protein complex, in response to a proton gradient and/or surface electrical field generated most effectively by photosystem I. x y l a k o i d membranes and their component complexes un- dynamic events is far from complete owing to a limited dergo conformational changes in response to illumination [see review by Barber (1982)l. Current understanding of these +Thiswork was carried out under the auspices of the US. Department of Energy, with funding from its Office of Basic Energy Sciences, Di- vision of Biological Energy Research, and from its Office of Health and Environmental Research. Additional funding was received under Re- search Grant 21 1.81 from the North Atlantic Treaty Organization. *Present address: Institute of Plant Physiology, Biological Research Center, Hungarian Academy of Sciences, Szeged, H-6701, Hungary. Present address: Research Institute for Photosynthesis, University of Sheffield, Sheffield S10 2TN, U.K. availability of techniques suited to the study of ultrastructural rearrangements within membranes. In the preceding paper (Garab et al., 1988), we showed that the circular dichroism (CD)' of thylakoids is sensitive to the ' Abbreviations: CD, circular dichroism; CDA, circular dichroism of absorbance; CDS, circular differential scattering; Chl, chlorophyll; DCMU, 3-(3,4-dichlorophenyl)-l,l-dimethylurea; LHC, light-harvesting chlorophyll a/b pigment-protein complex of photosystem 11; PMS, N- methylphenazonium methosulfate; FCCP, carbonyl cyanide p-(tri- fluoromethy1)phenylhydrazone. 0006-2960/88/0427-2430$01.50/0 zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA 0 1988 American Chemical Society