Phycobilisome Composition and Relationship to Reaction Centers in Anacystis Nidulans

Summary

Phycobilisomes were studied in Anacystis nidulans wild type and several spontaneous mutants selected for improved growth in far-red light (>650 nm). In the mutants the phycocyanin varied in relation to allophycocyanin but there was no alteration in the antenna size in terms of chlorophylls in photosystems I and II. Phycobilisomes of wild-type contained phycocyanin and allophycocyanin in a molar ratio of 3:1. Phycobilisomes of the mutants 85Y, 19Y and 59G had respective ratios of 0.4:1, 0.7:1, and 1:1. Analysis of purified phycobilisomes on SDS-PAGE gradient gels revealed significant differences in the polypeptide pattern. A comparison of phycobilisomes of the wild-type and 85Y by electron microscopy, showed that they were larger in wild-type (57nm × 30nm) than in 85Y (28nm × 15nm). The number of phycobilisomes per cell (~2 × 10⁴) was about the same in wild-type (white light) and 85Y (far-red light). The ratio of phycobilisome/reaction center 2 was close to 1 and was relatively constant in spite of large variations in chlorophyll and in phycocyanin content.