CHARACTERISTICS OF A LIGHT-DEPENDENT PROTON TRANSPORT IN CELLS OF RHODOSPIRILLUM RUBRUM

Suspensions of cells of Rhodospirillum rubrum harvested in the logarithmic phase of growth show a light-induced decrease of pH, which is dependent upon the presence of salts of Li+, Na+, K+, Mn2+, Mg2+, or Ca2+. NH4Cl failed to increase the magnitude of the response. During the subsequent dark period, the pH of the medium increases. If the cells are suspended in 200 mM NaCl at pH 5.5 the decrease in the pH is complete in approx. 30 sec. The decrease in pH is inhibited if 3.3 μg/ml antimycin A or 10 μM carbonylcyanide-m-chlorophenylhydrazone (CCCP) are added prior to illumination. If CCCP is added during the subsequent dark period there is a stimulation of the rise in pH. The effect of light intensity and initial pH on the pH response has been studied. © 1969.