The role of magnesium in the hydrolysis of sodium pyrophosphate by inorganic pyrophosphatase.

1. A polarographic method of measuring and continuously recording the concentration of oxygen in solution down to the order of 1O-9M has been described. 2. This method has been used to determine the respiration rate of bacteria as a function of oxygen concentration. 3. The results so obtained have shown that the respiration rate of bacteria is related to the oxygen concentration by the Michaelis-Menten equation, and the characteristic Km's of a number of organisms have been determined. 4. The effect of temperature and pH changes on the Km have been investigated. 5. Reasons for the differences in the Km's of different organisms have been discussed and an empirical equation relating Km to the size of the organism has been established.