Family II pyrophosphatases from photosynthetic bacteria can hydrolyze free pyrophosphate

Abstract

The hydrolytic activity from three partially purified family II pyrophosphatases from the photosynthetic bacteria Rhodobacter sphaeroides, Rhodobacter capsulatus, and Rhodovulum sulfidophilum, as well as the recombinant cytoplasmic pyrophosphatase from Rba. sphaeroides, was tested with Mg 2+-PPi, Mn 2+-PPi, and PPi 4-. Unlike family I pyrophosphatases that hydrolyze only the Mg 2+-PPi complex like those from Rhodospirillum rubrum, all family II enzymes tested showed hydrolytic activity with Mg 2+-PPi, Mn 2+-PPi, and PPi 4without cation. The activity without added cation remained the same, even under exhaustive dialysis or after desalting the enzyme through a Sephadex G-25 column. However, this activity disappeared upon the addition of ethylenediaminetetraacetic acid and could not be restored by adding Mg 2+. Moreover, the enzyme inactivation was not related to dissociation into lower molecular subunits as in other family II enzymes. This is the first report on pyrophosphatases that can hydrolyze pyrophosphate without a divalent cation added and that presumably contain a tightly bound divalent cation in their structure.