Comparative immunological detection of lipids and carotenoids on peptides of photosystem I from higher plants and cyanobacteria.

Abstract

Photosystem I preparations were obtained from wild-type tobacco Nicotiana tabacum var. JWB, three chlorophyll-deficient tobacco mutants: Su/su, Su/su var. Aurea and yellow-green leaf patches of the variegated mutant NC 95, Spinacia oleracea and furthermore from the mesophilic cyanobacterium Synechococcus PCC 7942 and the thermophilic cyanobacterium Synechococcus sp.. Peptides from these preparations were analyzed by SDS polyacrylamide gel electrophoresis and transferred for detection of bound lipids and carotenoids according to the Western blot procedure to nitrocellulose membranes. The PS I preparations from the Nicotiana tabacum species and spinach consist of the core complex and the LHCP I complex, the latter containing, however, traces of the LHCP II polypeptides. The core complex consists of the two core peptides with the apparent molecular mass of 66 kDa each and peptides with molecular masses of 22, 20, 19, 17, 16, 10 and 9 kDa. The LHCP I complex contains 4 subunits with molecular masses of 28, 26, 25 and 24 kDa. The PS I preparations of the two mutants Su/su and Su/su var. Aurea contain as impurities traces of the core peptides (D1/D2) and the two chlorophyll-binding peptides (CP43/CP47) of photosystem II. The PS I preparation from the mesophilic and thermophilic cyanobacterium consists of the two core peptides with the apparent molecular mass of 66 kDa and peptides with molecular masses of 16, 14 and 10 kDa. The peptides of the PS I preparations were characterized by specific PS I, CP I and LHCP I antisera. The antiserum to the PS I complex reacts in the Western blot with the homologous peptides of PS I from higher plants, but only with the CP I complex from the two cyanobacteria. In comparative studies with PS II from higher plants the PS I antiserum reacts with the LHCP II complex as expected. The antiserum to the CP I complex reacts only with the 66 kDa peptides of PS I from all objects. There is no cross reaction with the 66 kDa peptides (heterodimer of the D1/D2 peptides) of PS II. The antiserum to the LHCP I complex reacts only with the four LHCP I peptides of PS I from higher plants and as expected with the LHCP II of PS II: Because cyanobacteria do not have LHCP complexes, there is no reaction with the LHCP I antiserum. By means of polyclonal monospecific antisera to lipids it was shown by Western blot procedure that only two lipid species are bound to PS I peptides. The galactolipid monogalactosyldiglyceride is bound to the CP I complex of the Nicotiana tabacum species, spinach and the two cyanobacteria as well as to the LHCP I complex of the higher plants. The phospholipid phosphatidylglycerol is only associated with the CP I complex of the analyzed higher plants and cyanobacteria. With polyclonal monospecific antisera to carotenoids it was demonstrated that beta-carotene, lutein, neoxanthin and zeaxanthin are associated with the CP I complex of the higher plants and the cyanobacteria analyzed. Violaxanthin is also bound to the CP I complex of the two cyanobacteria, whereas it is bound together with neoxanthin to the LHCP I complex of the higher plants.