Respiration, cyanide‐insensitive oxygen uptake and oxidative phosphorylation in cyanobacteria

Cyanide‐insensitive oxygen uptake in the dark of 9 species of cyanobacteria was 6–20% of the total oxygen uptake of intact cells. In Phormidium, no cyanideinsensitive oxygen uptake was observed. In intact cells, the I₅₀ value for cyanide was significantly lower in cyanobacteria of the taxonomic sections I to III (1–9 μM) than in those from section IV and V (10–60 μM). Cyanide‐insensitive oxygen uptake in the cell‐free system of Anabaena variabilis was not affected by typical inhibitors of the alternative pathway of plants. Cell‐free oxidation of cytochrome c was completely inhibited by cyanide with an I₅₀ value of 0.5–1 μM. Electron transport of intact cells without cyanide present yielded P/O ratios of 0.7–3.0. The data on oxidative phosphorylation using intact cells and the cell‐free system, indicate that cyanide‐insensitive oxygen uptake is not coupled to ATP formation.