Reversible changes in macroorganization of the light-harvesting chlorophyll a/b pigment-protein complex detected by circular dichroism

Journal Article · Tue Apr 05 04:00:00 EDT 1988 · Biochemistry; (United States)

DOI:https://doi.org/10.1021/bi00407a028· OSTI ID:5323096

Garab, G; Leegood, R C; Walker, D A; Sutherland, J C; Hind, G

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 II and can drive a 40-80% decrease in CD signal relative to the dark control level. (iii) Photosystem I driven changes are fully inhibited by nigericin or NH/sub 4/Cl but are largely insensitive to gramicidin. CD changes driven by photosystem II, 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. 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.

• Research Organization: Brookhaven National Lab., Upton, NY (USA)
• OSTI ID: 5323096
• Journal Information: Biochemistry; (United States), Journal Name: Biochemistry; (United States) Vol. 27:7; ISSN BICHA
• Country of Publication: United States
• Language: English

Related Subjects

14 SOLAR ENERGY
140505* -- Solar Energy Conversion-- Photochemical
Photobiological
& Thermochemical Conversion-- (1980-)
CARBOXYLIC ACIDS
CHLOROPHYLL
DICHROISM
ELECTROMAGNETIC RADIATION
FOOD
HETEROCYCLIC ACIDS
HETEROCYCLIC COMPOUNDS
MOLECULAR STRUCTURE
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
PHOTOSYNTHETIC REACTION CENTERS
PHYTOCHROMES
PIGMENTS
PLANTS
PORPHYRINS
PROTEINS
RADIATIONS
SPINACH
VEGETABLES
VISIBLE RADIATION