The catalytic mechanism of valyl-tRNA synthetase from @entity375 has been investigated by pre-steady-state and steady-state kinetic measurements and end product dissociation studies. The pre-steady-state kinetics show a lag period during the early time when the reaction is started with free enzyme. The preincubation of the synthetase with tRNAVal and/or @entity4857 or preformation of @entity2596 approximately @entity860 leads to a progressive suppression of the lag. This lag probably reflects conformational transitions of the enzyme-substrate complex necessary for the transfer. At low pH or at a low ionic strength, the tRNAVal charging occurs much faster at the pre steady state than at the steady state. We show that after the fast transfer of @entity4857 from @entity1920 to tRNAVal, followed by the fast dissociation of @entity860 and @entity7371 , a new @entity1920 is synthesized which promotes the dissociation of the nascent @entity2596 -tRNAVal. This dissociation occurs in a multistep process. First @entity855 and @entity1760 promote the ejection of the @entity4857 moiety of @entity2596 -tRNAVal from the @entity1920 site. A new @entity1920 is then synthesized which promotes, in the presence of @entity1760 , several state changes of the end product complex. A complex is finally generated in which the enzyme-bound @entity2596 -tRNAVal is able to exchange rapidly with a tRNAVal molecule. The free tRNAVal plays an active role in this exchange. Depending upon the experimental conditions, one of these steps can determine the steady-state rate of tRNAVal charging. The dissociations of enzyme-bound uncharged tRNAVal or aa-tRNAs substituted on the @entity535 or on the tRNA parts by noncognate parts as well as the effect of the replacement of the adenylates by wrong adenylates have been investigated. It is shown that the @entity4857 and the tRNA moieties of @entity2596 -tRNAVal and the @entity4857 moiety of the @entity1920 are involved in this mechanism of dissociation. Finally, the rate-determining step of the reversal of tRNAVal charging at the steady-state has been investigated. It is shown that this step is the dissociation of the deacylated tRNAVal from enzyme.

Catalytic mechanism of valyl-tRNA synthetase from XXXX . Reaction pathway and rate-determining step in the aminoacylation of tRNAVal.

@entity7371 :: ('CHEBI:60614', 'Chemical') :: ['PPi'] @entity535 :: ('CHEBI:33704', 'Chemical') :: ['amino acid'] @entity2596 :: ('CHEBI:16414', 'Chemical') :: ['Val'] @entity1920 :: ('CHEBI:16027', 'Chemical') :: ['adenylate'] @entity4857 :: ('CHEBI:27266', 'Chemical') :: ['valine'] @entity860 :: ('MESH:D000249', 'Chemical') :: ['AMP'] @entity375 :: ('4932', 'Species') :: ["baker's yeast"] @entity855 :: ('MESH:D000255', 'Chemical') :: ['ATP'] @entity1760 :: ('MESH:D008274', 'Chemical') :: ['magnesium']
@entity375 :: (4932,Species) :: ['baker's yeast']
