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Iron-Sulfur Centers and Activities of the Photosynthetic Electron Transport Chain in Iron-Deficient Cultures of the Blue-Green Alga Aphanocapsa¹

Division of Molecular Plant Biology, University of California, Berkeley, California 94720

Cultures of the blue-green alga, Aphanocapsa, were grown under iron-limiting conditions and changes in concentration of redox components of the photosynthetic electron transport chain, particularly iron-sulfur centers, were monitored by spectroscopic methods. A moderate iron depletion (1/10 of the normal concentration) had little effect on photosynthetic electron transport reactions and growth. Nevertheless, the amount of membrane-bound non-heme iron decreased sharply, and ferredoxin was nearly totally replaced by a flavin-containing protein, flavodoxin. Severe iron-deficiency (1/100 of the normal concentration) was accompanied by growth inhibition and decreased rates of photosynthetic electron flow. The Photosystem I reaction center was most affected by iron depletion as evidenced by a decrease in the amounts of iron-sulfur centers A, B, and X. However, formation of other redox proteins, even those that do not contain iron, was also inhibited by severe iron deficiency.

¹ Supported in part by grants from the National Institutes of Health and the National Science Foundation to R.M. and a fellowship from the Deutsche Forschungsgemeinschaft to G. S.