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One of the components of the electron transport chain in chloro-plasts. Ferredoxins are nonhaem iron-sulphur proteins, i.e. they utilize an iron-containing reaction centre but the structure is not that of a haem, as in cytochromes, but iron and acid-labile sulphur are present instead. In chloro-plasts ferredoxin mediates the transfer of electrons between photosystem I and the ultimate electron acceptor, NADP. It accepts an electron, via a ferredoxin reducing substance, from the excited P700 chlorophyll a molecule, and transfers it, through a reaction catalysed by ferredoxin-NADP reductase, to NADP. Bacteria and animals also contain iron-sulphur proteins, some free in solution and some membrane bound.
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