The Rate-Determining Step on the recA Protein-Catalyzed ssDNA-Dependent ATP Hydrolysis Reaction Pathway
| Autor: | Einar Stole, Floyd R. Bryant |
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| Rok vydání: | 1997 |
| Předmět: | |
| Zdroj: | Biochemistry. 36:3483-3490 |
| ISSN: | 1520-4995 0006-2960 |
| DOI: | 10.1021/bi962881l |
| Popis: | We recently constructed a mutant recA protein in which His 163 was replaced by a tryptophan residue. The [H163W]recA protein is functionally identical to the wild-type protein, and the Trp163 side chain serves as a fluorescence reporter group for the ATP and ATPgammaS-mediated conformational transitions of the [H163W]recA-ssDNA complex. In this report, the pre-steady-state kinetics of the ATP and ATPgammaS-mediated transitions were examined by stopped-flow fluorescence. The kinetics of the ATP-mediated fluorescence change were consistent with a two-step mechanism in which an initial rapid equilibrium binding of ATP to the recA-ssDNA complex is followed by a first-order isomerization of the complex to a new conformational state; the rate constant for the isomerization step of 18 min is identical to the steady-state turnover number for ATP hydrolysis. The kinetics of the ATPgammaS-mediated fluorescence change were also consistent with a two-step binding mechanism with a unimolecular isomerization of 18 min(-1); since ATPgammaS is not hydrolyzed appreciably on the time scale of these experiments (0.017 min(-1)), this indicates that the isomerization step follows ATPgammaS (or ATP) binding but precedes ATPgammaS (or ATP) hydrolysis. These and other results are consistent with a kinetic model in which an ATP-mediated isomerization of the recA-ssDNA complex is the rate-determining step on the recA protein-catalyzed ssDNA-dependent ATP hydrolysis reaction pathway. |
| Databáze: | OpenAIRE |
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