Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UNIPROT:P20020 (adenosine triphosphatase)
 3,299 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

In combination with the Mo-Fe protein of nitrogenase from Klebsiella pneumoniae, the Fe protein of nitrogenase from Clostridium pasteurianum forms an active enzyme with novel properties different from those of either of the homologous nitrogenases. The steady-state rates of reduction of acetylene and H+ are 12% of those of the homologous system from C.pasteurianim. Acetylene reductase activity exhibited an approx. 10min lag at 30 degrees C before the rate of reduction became linear, consistent with a once-only activation step being necessary for acetylene reduction to occur. No such lag was observed for H2 evolution. The activity with N2 as a reducible substrate was very low, implying that acetylene reductase activity is not necessarily an accurate indication of nitrogen-fixing ability. This is of particular relevance to studies on mutant and agronomically important organisms. Stopped-flow spectrophotometric studies showed unimolecular electron transfer from the Fe protein to the Mo-Fe protein to occur at the same rate (k2 = 2.5 X 10(2)s-1) and with the same dependence on ATP concentration (apparent KD = 400 muM) as with the homologous Klebsiella nitrogenase. However, an ATP/2e ratio of 50 was obtained for H2 evolution, indicating that ATP hydrolysis had been uncoupled from electron transfer to substrate. These data indicate that ATP has at least two roles in the mechanism of nitrogenase action. The combination of the Mo-Fe protein of nitrogenase of C.pasteurianim and the Fe protein of K.pneumoniae were inactive in all the above reactions, except for a weak adenosine triphosphatase activity, 0.5% of that of the homologous K.pneumoniae system.
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PMID:Nitrogenases from Klebsiella pneumoniae and Clostridium pasteurianum. Kinetic investigations of cross-reactions as a probe of the enzyme mechanism. 13

Adenosine triphosphate (ATP) hydrolysis in the nitrogenase complex controls the cycle of association and dissociation between the electron donor adenosine triphosphatase (ATPase) (Fe-protein) and its target catalytic protein (MoFe-protein), driving the reduction of dinitrogen into ammonia. Crystal structures in different nucleotide states have been determined that identify conformational changes in the nitrogenase complex during ATP turnover. These structures reveal distinct and mutually exclusive interaction sites on the MoFe-protein surface that are selectively populated, depending on the Fe-protein nucleotide state. A consequence of these different docking geometries is that the distance between redox cofactors, a critical determinant of the intermolecular electron transfer rate, is coupled to the nucleotide state. More generally, stabilization of distinct docking geometries by different nucleotide states, as seen for nitrogenase, could enable nucleotide hydrolysis to drive the relative motion of protein partners in molecular motors and other systems.
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PMID:Nitrogenase complexes: multiple docking sites for a nucleotide switch protein. 1612 1