Abstract
Abstract The inhibitory effects of copper ion (Cu2+) on the photosynthetic electron transport function was investigated both in NaCl washed (depleted in 17 and 23 kDa polypeptides) and native (unwashed) photosystem II membrane preparations from spinach (Beta vulgaris) chlo-roplasts. Copper in the range of 2.0 to 15 μᴍ strongly inhibited the electron flow from water to 2,6-dichlorobenzoquinone in NaCl washed particles in a concentration dependent manner. Com plete inhibition was noticed at 15 μᴍ Cu2+. Oppositely in native membranes, 15 μᴍ C u2+ inhibited only 10-12% of control activity. It was found that calcium ion (Ca2+) significantly reduced the Cu2+ inhibition of electron transport activity. The Ca2+ supported prevention of Cu2+ toxicity was specific to Ca2+. Further analysis indicated that both Cu2+ and Ca2+ act competitively. Since Ca2+ is known to have stimulating/stabilizing effect at the donor side of photosystem II, it is therefore suggested that Cu2+ in NaCl washed particles exerts its inhibitory effect(s) at the oxidizing side of photosystem stimulates/stabilizes the oxygen evolution.
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