THE ATPASES OF PROPIONIGENIUM-MODESTUM AND BACILLUS-ALCALOPHILUS - STRATEGIES FOR ATP SYNTHESIS UNDER LOW-ENERGY CONDITIONS

In Propionigenium modestum, ATP synthesis is coupled via DELTA-muNa+ to the decarboxylation of (S)-methylmalonyl-CoA. The low energy yield of this reaction implies that approx. 4 decarboxylation cycles are necessary to synthesize 1 molecule of ATP. Theoretical considerations in accord with experimental results suggest ATP synthesis in P. modestum at DELTA-muNa+ = - 110 mV. Other anaerobic bacteria synthesize ATP at a DELTA-muH+ of similar size and alkaliphilic bacteria at pH 10.3 have a DELTA-muH+ of only - 103 mV. In these cases, the H+(Na+) to ATP stoichiometry must be at least 4.