Energy production in Ureaplasma urealyticum

Ureaplasma urealyticum lacks the conventional mechanisms for adenosine 5-triphosphate (ATP) generation, such as glycolysis or arginine breakdown, present in other mycoplasmas. The possibility that ATP may be generated in these organisms through the formation of an ion gradient coupled to urea hydrolysis has been suggested by Masover and Hayflick (Ann NY Acad Sci 225:118-130, 1973). Our data have proved that ATP is produced when urea is added to resting ureaplasmal cells and its formation requires the concomitant activity of both cytoplasmic urease and membrane-bound ATPase and is drastically reduced by carbonylcyanide-m-chlorophenylhydrazine. Analysis of the optimal conditions for ATP synthesis in ureaplasmas indicates that this energetic process depends upon phosphate, urea, pH and ammonium ions in the reaction mixture. Particularly ammonium ions can interfere with the production of energy only when the starting pH is kept slightly basic. We have also shown that the changes in fluorescence intensity are directly related to the concentrations of the added urea and are inhibited by the presence of acetohydroxamic acid, carbonycyanide-m-chlorophenylhydrazine, and ammonium ions. It appears that urea hydrolysis can generate an electrical potential through NH4+ diffusion across the Ureaplasma membranes, but this diffusion is also dependent upon the external acidic pH of the reaction mixture.