pH dependence of chlorophyll states, protein structures and function of the PSII membranes

The effect of varying pH on the photosystem II (PSII) membrane was studied using absorption and steady-state fluorescerce spectroscopy, and using a variable fluorescence technique. pH variations induced significant changes in the chlorophyll states of the PSI I merrbrane, but no effect was seen on the chiorophyll fluorescerce parameter F
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Fm
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For acidic pH conditions, protein structures of the PSII membrane were slightly altered, whil st at alkaline pH levels, large changes in the protein structure of the PSII membrane were detected. The results indicate that the microenvi ronment around Cys in the PSII membrane is very susceptible to al kaline pH conditions, and that in the acid (4 pH < 7) and alkaline (9 pH>7) regions, pH variation has no effect on the protein structures of the PSII reaction center (RC).