Comparative assessment of inorganic pyrophosphate and pyrophosphatase levels ofEscherichia coli, Clostridium pasteurianum, andClostridium thermoaceticum

Pyrophosphatase (PPiase) specific activities were much higher in anaerobic cultures of Escherichia coli (0.54 units) than in Clostridium pasteurianum (0.067 units) and Clostridium thermoaceticum (0.017 units) (1 unit = 1 μmole PPi hydrolyzed/min per mg cell dry wt.), and were fairly constant throughout the growth of all three organisms. Conversely, intracellular levels of pyrophosphate (PPi) were very low and constant in E. coli throughout growth (0.3 mM), while those of C. pasteurianum and C. thermoaceticum were higher (1.44 and 0.8 mM, respectively) and peaked sharply during mid log-phase of growth. PPiase and intracellular PPi remained relatively constant in E. coli when grown aerobically or anaerobically, and when growth was in medium containing PPi as the sole source of supplemental phosphorus.