Manganese as a Cofactor in Photosynthetic Oxygen 



Evolution 



ERICH KESSLER,* Research Institutes {Pels Fund), University of Chicago, 



Chicago, Illinois 



Manganese deficiency has been known for a long time to be a 

 powerful inhibitor of photosynthesis in algae (1). Its effect on metab- 

 olism is unique in so far as only photosynthesis is affected and not 

 respiration or chlorophyll formation (2,3). The inhibition of photo- 

 synthesis can be relieved within a short time by an addition of man- 

 ganese (1-3); the degree of inhibition is independent of light in- 

 tensity (2,3). The latter observation suggests a similarity between 

 manganese deficiency and poisoning with hydroxylamine, a substance 

 known to be a specific inhibitor of the oxygen-evolving process of 

 photosynthesis (4,5). Therefore, Pirson suggested that manganese 

 might perhaps be involved in the oxygen-liberating system of photo- 

 synthesis (2). 



The process of photoreduction found in certain algae adapted to 

 hydrogen (6) affords a possibility to test this hypothesis. In this re- 

 action, the photochemical process and the reduction of CO2 are pre- 

 sumably the same as in ordinary photosynthesis; only the evolution 

 of oxygen is replaced by a reaction between its precursors and molec- 

 ular hydrogen activated by hydrogenase (6). Therefore, an in- 

 hibitor specific for oxygen evolution in photosynthesis should not 

 inhibit photoreduction and should, in addition, prevent the reversion 

 of photoreduction to photosynthesis with evolution of oxygen which 

 normally occurs at higher light intensities. This was shown to be the 

 case in algae poisoned with hydroxylamine, o-phenanthroline, and 

 phthiocol (4,7). 



The green alga, Ankistrodesmus hraunii, can be adapted to hy- 

 drogen within a few hours in an atmosphere of hydrogen -|- 4% 



* This work was performed during the tenure of a fellowship awarded by the 

 National Academy of Sciences and International Cooperation Administration. 

 Permanent address: Botanisches Institut, Universitat Marburg, Marburg/Lahn, 

 Germany. 



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