The Effect of Polyene Antibiotics on Photosynthetic Electron Transfer

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Abstract
The effect of four polyene antibiotics and digitonin on photosynthetic electron transfer by maize mesophyll chloroplasts has been investigated. All five compounds, at concentrations between 0.1 mM and 20 mM, inhibited photosystem 2 activity as measured by the photo-reduction of ferricyanide and 2,6-dichlorophenolindophenol from water. Etruscomycin, amphotericin B, and digitonin were more inhibitory than filipin and nystatin. Photosystem 1 activity was inhibited by 1 mM concentrations of etruscomycin, amphotericin B, and digitonin but not by filipin and nystatin. In all cases where inhibition occurred, it was temperature dependent. The inhibition of photosystem 1 activity could be relieved by plastocyanin. Etruscomycin and digitonin, at concentrations of 0.5 mM and above, caused disintegration of the chloroplasts, and this disintegration was accompanied by a two- to three-fold increase in photosystem 1 activity in the presence of plastocyanin. It is concluded that the action of polyene antibiotics results in the release of plastocyanin from its site in the photosynthetic electron transfer chain. The results are discussed in terms of the abilities of polyene antibiotics and digitonin to form complexes with sterols.

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