Surface charge modifications do not affect the hydrolytic activity of membrane-bound pyrophosphatase of Rhodospirillum rubrum.

The surface charge of the membrane of chromatophores of Rhodospirillum rubrum was modified by two methods: fusion of liposomes with the membrane of the chromatophore by changing the pH and by incubating chromatophores in the presence of cationic or anionic detergents. The hydrolytic activity of membrane-bound pyrophosphatase, on surface charge modified chromatophores, did not change the Km of the enzyme for its substrate (Mg-PPi2-) nor the activation effect of free Mg2+ on the hydrolytic activity. This membrane enzyme is not regulated by surface charge.