Signal II slow

The EPR spectrum arising from Z , the highly reactive and short-lived electron donor to P-680, is almost identical to that of another component, [182]. Unlike Z, however, D is extremely stable and is present in the dark in all untreated plant material. Various treatments remove the signal, presumably either by direct electron donation (incubation with DCIP -I- ascorbate) or by exposing this highly oxidizing component to the environment. When reduced, D can act as an electron 

Although its EPR spectrum is the same as that of it seems to be in an inequivalent position relative to the manganese of the 02-evolving enzyme since its EPR microwave power saturation characteristics are different but become similar upon removal of the Mn [187,200]. 

A signal lacking the characteristic line shape of Signal II slow was obtained by oxidation and attributed to in an environment modified by the strong oxidant potassium iridate [188]. It had a redox potential at pH 8.5 (oxidizing direction only) of 760 mV. The physiological role of D is not understood. 

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A Boussac and A Etienne (1984) Midpoint potential of signal II (slow) in Tris-washed photosystem-ll particles. Biochim Biophys Acta 766 576-581... 

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