Photosynthetic activity of diimidoester-modified cells, permeaplasts, and cell-free membrane fragments of the blue-green alga Anacystis nidulans.

On treating the blue green alga Anacystis nidulans with dimethylsuberimidate up to 70% of the free NH2 of the photosynthetic membrane is amidinated, and presumably inter- and intramolecular cross-links are established in the membrane proteins. Amidination destroys the ability of A. nidulans to photoreduce HCO3(-) but leaves the photochemical activities of Photosystems II and I nearly intact. With added electron acceptors, photosynthetic O2 evolution can be demonstrated both with permeable cells (permeaplasts) prepared by digestion of the cell wall of dimethylsuberimidate-reacted A. nidulans with lysozyme, as well as with heavy membrane particles (36 000 x g) prepared from dimethylsuberimidate-reacted cells. Permeaplasts prepared from dimethylsuberimidate-reacted cells resist damage in hypoosmotic medium, whereas those prepared from unreacted cells are induced to release C-phycocyanin. On the other hand, the former are inactivated more easily by heat stress than the latter. On this basis, it is concluded that cross-linking with dimethylsuberimidate confers functional instability to photosynthetic membranes.