Inhibition of photosynthetic electron transport in tobacco chloroplasts and thylakoids of the blue green alga Oscillatoria chalybea by an antiserum to synthetic zeaxanthin.

An antiserum to synthetic Zeaxanthin inhibits photosynthetic electron transport on the oxygen-evolving side of photosystem II in tobacco chloroplasts and thylakoids of the filamentous blue-green alga Oscillatoria chalybea. The inhibition site lies for both species between the site of electron donation of water or tetramethyl benzidine and that of diphenyl carbazide or manganese II ions. Typical photosystem I reactions are not impaired by the antiserum. The effect of the antiserum concerning the inhibition site is practically identical to that of the earlier described antiserum to violaxanthin. However, the degree of inhibition seems to be generally somewhat lower with the antiserum to Zeaxanthin, than with that to violaxanthin which hints at a lesser accessibility of zeaxanthin, in the tylakoid membrane in comparison to violaxanthin. In the course of these investigations new evidence was obtained that the oxygen-evolving side of the electron transport scheme is differently organized in Oscillatoria chalybea when compared to tobacco chloroplasts. Thus, the silicomolybdate reduction with water as the electron donor is sensitive to DCMU in these algae.