Cation activation of pyrophosphatases from soil microorganisms

The intracellular inorganic pyrophosphatases obtained from mixed cultures of soil microorganisms were characterised in terms of the activating cation and pH-activity profile. Microorganisms were grown in an initial culture 10 mm in tetrasodium pyrophosphate, a nutritionally non-specific aqueous medium, buffered at pH 7.0 with an organic buffer and inoculated with soil. The intracellular pyrophosphatases in a desalted, cell-free enzyme preparation were examined for activity in assays using 1 mM tetrasodium pyrophosphate and nine cations (Mg²⁺, Zn²⁺, Co²⁺, Mn²⁺, Fe²⁺, Ca²⁺, Cu²⁺, Al³⁺ and Fe³⁺) over the pH range 2–10, with appropriate buffers. Only the first 5 cations activated the enzymes. The pH-activity profiles for each cation were different and each displayed only one pH optimum. The pH optima were not greatly affected by cation concentration or kind of buffer. The specific activities at the optimum pH and cation concentration for each culture decreased in order Mg²⁺ > Zn²⁺ > Co²⁺ > Mn²⁺ > Fe²⁺. The results indicate the production of functionally similar enzymes by diverse microorganisms.