Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0392674 (exhaustion)
 13,658 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

1. Formycin triphosphate (FTP), a fluorescent analogue of ATP, is a substrate for (Na+ + K+)-ATPase (ATP phosphohydrolase, EC 3.6.1.3), with properties similar to those of ATP. 2. FTP and formycin diphosphate (FDP) bind to the enzyme with high affinity and, on binding, the nucleotide fluorescence is enhanced 3-4-fold. It is therefore possible, with a stopped-flow fluorimeter, to measure the rates of binding and release of FTP and FDP under conditions in which turnover does not occur. 3. When the enzyme-FTP complex is exposed to conditions permitting turnover (Mg2+, Na+ +/- K+), changes in fluorescence occur which can be explained by supposing that they reflect the interconversion of states with or without bound nucleotides. A rapid fall in fluorescence, that we attribute to the rapid release of FDP from newly phosphorylated enzyme, is followed by a steady state in which low fluorescence suggests that little nucleotide is bound. Eventually, exhaustion of FTP allows rebinding of FDP to the enzyme, which is signalled by a rise in fluorescence. 4. The estimated rate of FDP release from newly formed phosphoenzyme is unaffected by the presence of K+ (0-2 mM) or the concentration of FTP (1-20 micron). 5. Experiments with [gamma-32P]FTP show that about 1 mol of 32P is incorporated per mol of enzyme. The rate of phosphorylation of the enzyme by [gamma-32P]FTP has been measured with a rapid-mixing-and-quenching apparatus. 6. Kinetic data from the fluorescence and phosphorylation experiments show that the behaviour of the enzyme, at least at the low nucleotide concentrations employed, is consistent with the Albers-Post model, and is difficult to reconcile with models in which K+ acts at or before the step in which FDP is released during turnover.
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PMID:Elementary steps of the (Na+ + K+)-ATPase mechanism, studied with formycin nucleotides. 21 Aug 11

The addition of methanol to a cell suspension of Methanosarcina barkeri resulted in an increase of the intracellular ATP concentration from 1 nmol/mg to 10 nmol/mg protein and in the formation of a proton-motive force delta p of -130 mV. delta p consisted of more than 90% of the membrane potential delta psi. These values were similar under N2 and under H2. The addition of the uncoupler tetrachlorosalicylanilide to the above system under N2 led to a drastic decrease of both, the ATP concentration and the delta p and to a stop of methanogenesis. With methanol and H2, however, methane formation continued, although the effect of the uncoupler on the ATP pool and on delta p was a under N2. The proton-translocating ATPase inhibitor N,N'-dicyclohexylcarbodiimide caused a rapid exhaustion of the ATP pool and a discontinuation of methane synthesis, whereas delta p was unaffected. Inhibition of methane formation under these conditions could be relieved by the addition of the uncoupler tetrachlorosalicylanilide. These results demonstrate that methane formation according to the equation CH3OH + H2----H2----CH4 + H2O was coupled to ATP synthesis by a chemiosmotic mechanism and was under the control of delta psi: Methane formation only proceeded if the delta psi generated was used for ATP synthesis or if an uncoupler was present. Under N2, methane formation according to the equation 4CH3OH ----CO2 + 3CH4 + 2H2O was abolished by an uncoupler, because one step in the oxidation of methanol to 1 CO2 apparently depended on an energized state of the membrane.
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PMID:Coupling of ATP synthesis and methane formation from methanol and molecular hydrogen in Methanosarcina barkeri. 632 9