Simultaneous detection of spin-coupled and decoupled QA- EPR-signals in Photosystem II complexes isolated with isoelectric focusing

• The Photosystem II multisubunit protein complex can be extracted from thylakoid membranes with non-ionic detergents and subjected to various spectroscopical and biochemical investigations. This paper shows that after extraction with dodecyl-beta-D-maltoside, several Photosystem II complexes could be resolved by isoelectric focusing. Structurally, the various Photosystem II complexes differed from each other in polypeptide composition, especially with regard to the chlorophyll a/b-binding proteins, which gave rise to differing isoelectric points. Functionally, the various Photosystem II complexes differed from each other on the acceptor side, as judged by acceptor side-dependent electron transfer and electron paramagnetic resonance (EPR). The Q_{A}^- Fe2+-signal (g = 1.84), arising from Q_{A}^- spin-coupled to the acceptor-side iron, and a radical signal arising from decoupled Q_{A}^- (g = 2.0045) could be detected simultaneously in some of the Photosystem II complexes, and the amount of each of the two signals were inversely related. The results are discussed in relation to previously known heterogeneities in Photosystem II.

Ämnesord

NATURVETENSKAP  -- Biologi (hsv//swe)

NATURAL SCIENCES  -- Biological Sciences (hsv//eng)

Nyckelord

EPR

IEF

polypeptide composition

PS II core

PS II heterogeneity

Q_{A}

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