Energy production in Ureaplasma urealyticum

Romano, Nicholas; Licata, R La; Alesi, D Russo

doi:10.1097/00006454-198611010-00024

Cited by 27 publications

(16 citation statements)

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“…These data extend a previous report that gave qualitative information that the addition of urea to a suspension of U. urealyticum increased membrane potential (19). The increase in both Adj and ApH was totally abolished by the addition of flurofamide, thus demonstrating that urea hydrolysis is, at a minimum, related to the increase in Ap.…”

Section: Resultssupporting

confidence: 89%

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Hydrolysis of urea by Ureaplasma urealyticum generates a transmembrane potential with resultant ATP synthesis

et al. 1993

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When urea is added to Ureaplasma urealyticum, it is hydrolysed internally by a cytosolic urease. Under our measuring conditions, and at an external pH of 6.0, urea hydrolysis caused an ammonia chemical potential equivalent to almost 80 mV and, simultaneously, an increase in proton electrochemical potential (h) of about 24 mV with resultant de novo ATP synthesis. Inhibition of the urease with the potent inhibitor flurofamide abolished both the chemical potential and the increase of Ap such that ATP synthesis was reduced to -5% of normally obtained levels. Uncouplers of electrochemical gradients had little or no effect on these systems. The electrochemical parameters and ATP synthesis were measured similarly at three other external pH values. Any change in Ap was primarily via membrane potential (A*), and the level of de novo ATP synthesis was related to the increase in Ap generated upon addition of urea and more closely to the ammonia chemical potential.Although the organisms lack an effective mechanism for internal pH homeostasis, they maintained a constant ApH. The data reported are consistent with, and give evidence for, the direct involvement of a chemiosmotic mechanism in the generation of around 95% of the ATP by this organism. Furthermore, the data suggest that the ATP-generating system is coupled to urea hydrolysis by the cytosolic urease via an ammonia chemical potential.

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Section: Resultssupporting

confidence: 89%

“…ATP synthesis, however, correlated to some extent with the differential in Ap (in the presence or absence of urea; see below). The predominant component in the elevation of Ap values is Al, which contrasts with previous observations that ApH is the more significant factor (19,21).…”

Section: Resultscontrasting

confidence: 88%

Hydrolysis of urea by Ureaplasma urealyticum generates a transmembrane potential with resultant ATP synthesis

et al. 1993

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“…As shown in Table 3, significant differences in intracellular potassium and ammonium concentrations were observed in cells grown at different urea concentrations. For Ureaplasma urealyticum, ATP synthesis has been described as being coupled to a chemical potential of ammonium generated upon the addition of urea (24,25,28). When the transmembranic gradient of ammonium in B. pasteurii was determined under similar conditions, it was obvious that even if the intracellular ammonium concentration increased upon the addition of urea to resting cells grown at high urea concentrations, the concentration gradient (NH 4 ϩ in /NH 4 ϩ out , where NH 4 ϩ in and NH 4 ϩ out are intracellular and extracellular ammonium concentrations, respectively) was highest prior to the addition of urea (Table 4).…”

Section: Resultsmentioning

confidence: 99%

Ammonium/urea-dependent generation of a proton electrochemical potential and synthesis of ATP in Bacillus pasteurii

Jahns

1996

J Bacteriol

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The influence of ammonium and urea on the components of the proton electrochemical potential (⌬p) and de novo synthesis of ATP was studied with Bacillus pasteurii ATCC 11859. In washed cells grown at high urea concentrations, a ⌬p of ؊56 ؎ 29 mV, consisting of a membrane potential (⌬) of ؊228 ؎ 19 mV and of a transmembranic pH gradient (⌬pH) equivalent to 172 ؎ 38 mV, was measured. These cells contained only low amounts of potassium, and the addition of ammonium caused an immediate net decrease of both ⌬ and ⌬pH, resulting in a net increase of ⌬p of about 49 mV and de novo synthesis of ATP. Addition of urea and its subsequent hydrolysis to ammonium by the cytosolic urease also caused an increase of ⌬p and ATP synthesis; a net initial increase of ⌬, accompanied by a slower decrease of ⌬pH in this case, was observed. Cells grown at low concentrations of urea contained high amounts of potassium and maintained a ⌬p of ؊113 ؎ 26 mV, with a ⌬ of ؊228 ؎ 22 mV and a ⌬pH equivalent to 115 ؎ 20 mV. Addition of ammonium to such cells resulted in the net decrease of ⌬ and ⌬pH without a net increase in ⌬p or synthesis of ATP, whereas urea caused an increase of ⌬p and de novo synthesis of ATP, mainly because of a net increase of ⌬. The data reported in this work suggest that the ATP-generating system is coupled to urea hydrolysis via both an alkalinization of the cytoplasm by the ammonium generated in the urease reaction and a net increase of ⌬ that is probably due to an efflux of ammonium ions. Furthermore, the findings of this study show that potassium ions are involved in the regulation of the intracellular pH and that ammonium ions may functionally replace potassium to a certain extent in reducing the membrane potential and alkalinizing the cytoplasm.

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“…Urease activity has been detected in a large variety of bacteria (for references, see reference 16), but the ureaplasmas are the only organisms known to depend on urea for growth (6,9,29). Urea hydrolysis appears to play a major role in the energy metabolism of ureaplasmas by promoting ATP synthesis through a chemioosmotic mechanism (12,13,24,25). This rather unique energy-yielding mechanism is essential for the ureaplasmas, which are known to lack the major energy-yielding (glycolytic and arginine dihydrolase) pathways established so far for other mollicutes (19).…”

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confidence: 99%

Characteristics of Ureaplasma urealyticum urease

et al. 1988

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Sonication of Ureaplasma urealyticum cells grown in a dialysate growth medium effectively separated the cytoplasmic fraction from the membrane fraction, with both fractions relatively free from exogenous contaminating proteins. The urease activity was associated with the cytoplasmic fraction, and the ureaplasmal urease exhibited a specific activity higher than that of crystalline jack bean urease. The enzymatic activity of the ureaplasmal enzyme was optimum at pH 7.5 and was resistant to the chelating agents EDTA and sodium citrate. Sulfhydryl-blocking agents such as HgCl2 and Pb(NO3)2 inhibited the ureaplasmal urease, which was also shown to be particularly sensitive to flurofamide and, to a much lesser extent, to acetohydroxamic acid. Electrophoretic analysis of the proteins of the ureaplasmal cell fractions combined with Western immunoblot with an antiserum to the ureaplasmal urease indicated that the urease constitutes a major component of the cytoplasm and is composed of several 70-kilodalton polypeptides.Ureaplasma species differ from all other mycoplasmas (class Mollicutes) by possessing urease activity (32). Urease activity has been detected in a large variety of bacteria (for references, see reference 16), but the ureaplasmas are the only organisms known to depend on urea for growth (6,9,29). Urea hydrolysis appears to play a major role in the energy metabolism of ureaplasmas by promoting ATP synthesis through a chemioosmotic mechanism (12,13,24,25). This rather unique energy-yielding mechanism is essential for the ureaplasmas, which are known to lack the major energy-yielding (glycolytic and arginine dihydrolase) pathways established so far for other mollicutes (19). The fact that specific urease inhibitors inhibit the growth of ureaplasmas (5,8,14,26) supports the key role of urease in ureaplasmal growth.Despite the apparent importance of the ureaplasmal urease, our knowledge of the structure and properties of the enzyme is very fragmentary. Early attempts to characterize the enzyme in crude cell extracts (13,14,26,31), as well as more-recent efforts directed at purification of the enzyme (3, 30), encountered great difficulties because of the extremely low yields of ureaplasmas and the high level of contamination of the harvested organisms with foreign proteins from the growth medium (21). To overcome this problem, we employed large volumes of a dialysate broth medium (9) which yielded on harvest satisfactory amounts of cells relatively free of medium contaminants. By employing sonication as an effective means of lysing the cells and separating the cytoplasm from the membrane fraction and by using a sensitive and highly reproducible method for measuring rates of urease activity, we were able to improve considerably the definition of some of the structural and functional properties of the urease from the type strain (T960, serovar VIII) of human Ureaplasma urealyticum. MATERIALS AND METHODSOrganism and growth conditions. The type strain of U. urealyticum (T960, serovar VIII) was obtained from M. C. She...

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Energy production in Ureaplasma urealyticum

Cited by 27 publications

References 0 publications

Hydrolysis of urea by Ureaplasma urealyticum generates a transmembrane potential with resultant ATP synthesis

Hydrolysis of urea by Ureaplasma urealyticum generates a transmembrane potential with resultant ATP synthesis

Ammonium/urea-dependent generation of a proton electrochemical potential and synthesis of ATP in Bacillus pasteurii

Characteristics of Ureaplasma urealyticum urease

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