Inhibition of Photosystem II-Reactions in Blue-Green Algae by the Antisera to Lutein and Neoxanthin

An antiserum to lutein agglutinates thylakoids of N ostoc muscorum and O scillatoria chalybea. From this it follows that lutein is located in the outer surface of the thylakoid membrane of these blue-green algae. The same result is obtained for an antiserum to neoxanthin. As neoxanthin is supposed not to occur in blue-green algae it follows that in this case the antibody action should be directed towards a carotenoid with allenic structure. The antisera to lutein and neoxanthin inhibit in both investigated algal species photosynthetic electron transport on the oxygen-evolving side of photosystem II. Moreover, the inhibition sites of both antisera are identical in N ostoc m uscorum and are located between the sites of electron donation of the artificial electron donors tetramethyl benzidene and diphenylcarbazide. In the case of the blue-green alga O scillatoria chalybea the inhibition sites of both antisera differ. Whereas the inhibition site of the antiserum to neoxanthin lies again between the sites of electron donation of tetramethyl benzidine and di­ phenylcarbazide, the inhibition site of the antiserum to lutein appears to be situated at least partially beyond the site of electron donation of tetramethyl benzidine. The degree of inhibition of electron transport reactions with N ostoc muscorum is for both antisera 50 — 60 per cent and is pH-dependent. The pH-optimum lies at pH 7.2 for the antiserum to neoxanthin and at 7.8 for the antiserum to lutein. In comparison to this data the same antisera inhibit electron transport in chloroplasts from higher plants only by 20%. This low degree of inhibition in higher plants is apparently due to the fact that the surfaces of the thylakoids are not accessible to antibodies within the grana. In contrast to this the thylakoid surfaces of blue-green algae are fully accessible because the thylakoids are unstacked. The thylakoids of Oscillatoria chalybea have the tendency towards aggregation. Therefore, the results concerning the accessibility of the carotenoids to antibodies are not so clear cut as with N ostoc muscorum.