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Title: STABILIZATION OF THE HIGH POTENTIAL FORM OF CYTOCHROME B-559 BY CALCIUM OR LACK OF OXYGEN

Author
item MCNAMARA, V - UNIV OF ILLINOIS, URBANA
item GOUNARIS, K - IMPERIAL COLLEGE, LONDON
item WHITMARSH, CLIFFORD

Submitted to: Photosynthesis International Congress Symposium Proceedings and Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: 6/28/1995
Publication Date: N/A
Citation: N/A

Interpretive Summary:

Technical Abstract: Cytochrome b-559 is an essential component of the reaction center of Photosystem II although its role remains unresolved. In the dark, the predominant high redox potential form (cyt b-559HP) is associated exclusively with PSII complexes in granal domains of the thylakoid membrane whilst a low potential form (cyt b-559LP) is found only in stromal lamellae. Reversible interconversion between these two states has been speculated to occur as part of a mechanism by which cyt b-559LP protects PS II against photodamage. Cyt b-559HP is frequently found to correlate with the ability of PS II to evolve oxygen although a causal relationship is considered unlikely since extrinsic-polypeptide-depleted PS II can evolve oxygen if re-constituted with calcium while cyt b-559 remains in its low potential form. Using PS II-enriched membranes containing almost exclusively cyt b-559HP, it is shown that the binding of calcium is necessary but not sufficient to stabilize this form of the cytochrome. In contrast, the 23 kDa extrinsic polypeptide of PS II is not required. Furthermore, it is shown that oxygen is needed for the conversion to cyt b-559LP.