Chen X, Stitt BL. ADP but not P(i) dissociation contributes to rate limitation for Escherichia coli Rho.
J Biol Chem 2009;
284:33773-80. [PMID:
19837672 DOI:
10.1074/jbc.m109.056473]
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Abstract
To define the molecular mechanism by which ATP hydrolysis powers the 5'-->3' travel of homohexameric Escherichia coli transcription termination factor Rho along RNA, rates for association and dissociation of non-RNA substrates and products were measured. Rapid mix/chemical quench and stopped-flow spectrofluorometry measurements were carried out with Rho and [gamma-(32)P]ATP, mantADP, or fluorescently tagged E. coli phosphate-binding protein. The results indicate that the P(i) off-rate is not rate limiting, but at approximately 90 s(-1), the ADP dissociation rate is comparable to the 30 s(-1) k(cat). Previous results indicate that the chemistry step of ATP hydrolysis by Rho is at least 10-fold faster than the overall catalytic cycle. The as yet unmeasured RNA dissociation step, which could be associated with a protein conformation change, might also be a rate-limiting factor.
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