Helically organized macroaggregates of pigment-protein complexes in chloroplasts: evidence from circular intensity differential scattering

Abstract

Angle dependence of circular intensity differential scattering (CIDS) and of nonpolarized scattering was determined in isolated spinach chloroplasts at 514.5 nm. CIDS between 0.degree. and 170.degree. was independent of the nonpolarized scattering and showed intense lobes of alternating signs, exhibiting the negative and positive maxima around 15.degree. and 70.degree., respectively. These results provide experimental evidence for the existence of large helically organized macroaggregates of pigment-protein complexes in thylakoid membranes. Modeling of the CIDS data by a simple helical array of uniaxial polarizable groups suggests that the chiral structure is left-handed with pitch and radius of the order of 385 nm.