Reactions of Antisera to Lutein and Plastoquinone with Chloroplast Preparations and their Effects on Photosynthetic Electron Transport

An antiserum to lutein inhibits photosynthetic electron transport between water and potas­ sium ferricyanide in chloroplasts from green Nicotiana tabacum var. John William’s Breadleaf. However, electron transport between diphenylcarbazide and potassium ferricyanide is not impaired. From this it is concluded that the photochemically active carotenoid should feed its electrons into the photosynthetic electron transport chain before the site from which diphenyl­ carbazide donates electrons. The inhibition of the ferricyanide H ill reaction in chloroplasts by antibodies to lutein depends on the accessibility of the carotenoid antigen in the thylakoid membrane. In fresh preparations the accessibility is greater in chloroplasts in which photo­ synthetic electron transport is coupled to photophosphorylation. Concomitantly the antiserum to lutein agglutinates only such chloroplast preparations in which the H i l l reaction is im­ paired by the antiserum. An antiserum to plastoquinone inhibits ferricyanide photoreduction of chloroplasts regardless whether driven by water or diphenylcarbazide as the electron donors. Typical photosystemI-reactions are not influenced by the antiserum. In a certain type of chloroplast preparations the antiserum does not inhibit PMS-mediated photophosphorylation inferring that plastoquinone, eventually involved in this reaction, is either not accessible to antibodies, or that this cyclic electron flow does not necessarily pass through plastoquinone.