The effect of antibodies to neoxanthin on electron transport on the oxygen evolving side of photosystem II and the reactions of this antiserum with variuos chloroplast preparations.

Antibodies to neoxanthin agglutinate stroma-free swellable chloroplasts from tobacco (Nicotiana tabacum var. John William's Broadleaf) and Antirrhinum (Antirrhinum majus) whereas stroma-freed chloroplasts, which have lost the swellability are not agglutinated despite the fact that antibodies to neoxanthin are specifically absorbed. In this latter case the agglutination is hindered for sterical reasons. From this it is concluded that neoxanthin is located in the outer surface of the thylakoid membrane. The antiserum to neoxanthin inhibits the ferricyanide photo-reduction in chloroplasts when water is the electron donor by 15%. With diphenylcarbazide in tris-treated chloroplasts no inhibition is observed. Hence, just as in the case of the antiserum to lutein the site of inhibition is on the donor side of potosystem II namely between water and the site of electron donation of diphenylcarbazide. Benzidine/ascorbate is another artificial electron donor system of photosystem II reported in the literature. The photoreduction of anthraquinone-2-sulphonate with this donor system is inhibited. In contrast to the antiserum to lutein the antiserum to neoxanthin inhibits DCMU-sensitive photophosphorylation reactions in the system H2O leads to ferricyanide and benzidine/ascorbate leads to anthraquinone-2-sulphonate. Therefore, the electron transport coupled to photophosphorylation is inhibited by the antiserum.