Functional size analysis of pyrophosphatase from Rhodospirillum rubrum determined by radiation inactivation

A radiation inactivation technique was employed to determine the functional size of pyrophosphatase (PPase) from the chromatophores of Rhodospirillum rubrum . The activities of hydrolysis and synthesis reactions of pyrophosphatase and its coupled proton translocation decayed in a simple exponential function with the increase of radiation dosages. D 3 , values of 5.2 ± 0.7 and 5.8 ± 0.8 Mrads were obtained for pyrophosphate hydrolysis and its associated proton translocation yielding molecular masses of 167.7 ± 30.7 and 156.3 ± 26.6 kDa, respectively. Similarly, a D 3 , value of 4.4 ± 0.6 Mrads was measured for the acid‐base induced pyrophosphate synthesis resulting in a radiation sensitive size of 196.3 ± 31.9 kDa.