| Abstract: | In the cells of the phototrophic bacteria Rhodospirillum rubrum and Rhodopseudomonas palustris the two enzymes of the cAMP system enzymes - adenylate cyclase and cAMP phosphodiesterase (PDE) exist in a soluble and membrane-bound forms. After mild disruption of the cells (sonication up to 3 min) the activity of both enzymes is found in the chromatophores. In the cells of the two types of bacteria grown under anaerobic conditions soluble adenylate cyclase is predominant. In the cells of R. rubrum the soluble form of PDE posesses higher activity, whereas in the cells of Rh. palustris a higher activity is observed in the membrane-bound form. In addition to their different localization in the cells, the PDE forms of Rh. rubrum differ in their ratios to the concentrations of hydrogen ions and bivalent metals; the latter difference, however, may be accounted for by the effect of a protein modulator of PDE. The pH optimum of membrane-bound PDE is 9.15. Soluble PDE has two activity maxima at pH 7.5 and 8.7. It is probable that similar to the animal tissue enzyme, PDE from Rh. rubrum exists in the soluble phase in at least tw forms. Close pH optima for soluble adenylate cyclase and for one of the soluble PDE forms (about 8.5) may indicate the unidirectional control of these enzymes by hydrogen ion concentration. |
