HYPOTHESIS - THE PHYSIOLOGICAL-ROLE OF THE MEMBRANE-BOUND PROTON-TRANSLOCATING PYROPHOSPHATASE IN SOME PHOTOTROPHIC BACTERIA

A hypothesis is formulated in which a physiological role for the membrane-bound proton-translocating pyrophosphatase (H+-PPase) in some phototrophic bacteria is put forward. The main task for this enzyme is to maintain a substantial protonmotive force under circumstances of lower energy, e.g. in darkness. Granules containing pyrophosphate (PP(i)) are proposed to be the source of hydrolyzable free PP(i). Under conditions of ample energy, for instance in high light, the H+-PPase, together with other PP(i)-producing enzymes in the cell, provide PP(i) for re-formation of the phosphate-containing granules, i.e. the H+-PPase is a PP(i) synthesizer during illumination. The hypothesis is discussed in connection with present knowledge.