Soluble inorganic pyrophosphatases (inorganic diphosphatases, EC ) were isolated and characterized from three phylogenetically diverse cyano-bacteria)Synechocystis sp. PCC 6803, Anabaena sp. PCC 7120, and Pseudanabaenasp. PCC 6903 – and one anoxygenic photosynthetic bacter-ium, Rhodopseudomonas viridis(purple nonsulfur).