[2]Rotaxane Formation by Transition State Stabilization

Transition state stabilization by a catalytic RNA.

The hairpin ribozyme catalyzes sequence-specific cleavage of RNA through transesterification of the scissile phosphate. Vanadate has previously been used as a transition state mimic of protein enzymes that catalyze the same reaction. Comparison of the 2.2 angstrom resolution structure of a vanadate-hairpin ribozyme complex with structures of precursor and product complexes reveals a rigid activ...

Transition-state stabilization in the mechanism of tyrosyl-tRNA synthetase revealed by protein engineering.

The principal catalytic factor in the activation of tyrosine by the tyrosyl-tRNA synthetase is found to be improved binding of ATP in the transition state. The activation reaction involves the attack of the tyrosyl carboxylate on the alpha-phosphate group of ATP to generate a pentacoordinate transition state. Model building of this complex located a binding site for the gamma-phosphate group of...

Transition state stabilization by chloramphenicol acetyltransferase. Role of a water molecule bound to threonine 174.

The structure of the type III variant of chloramphenicol acetyltransferase reveals that Thr-174, a conserved residue, is hydrogen-bonded to a bound water molecule (water 252). Modeling studies (P. C. E. Moody and A. G. W. Leslie, unpublished data) suggested that water 252 could play a part in transition state stabilization via a hydrogen bond to the oxyanion of the putative tetrahedral intermed...

RNA catalysis by a group I ribozyme. Developing a model for transition state stabilization.

Substrate activation by acyl-CoA dehydrogenases: transition-state stabilization and pKs of involved functional groups.

The mechanism by which acyl-CoA dehydrogenases initiate catalysis was studied by using p-substituted phenylacetyl-CoAs (substituents-NO2, -CN, and CH3CO-), 3S-C8-, and 3'-dephospho-3S-C8CoA. These analogues lack a beta C-H and cannot undergo alpha,beta-dehydrogenation. Instead they deprotonate at alpha C-H at pH > or = 14 to form delocalized carbanions having strong absorbancies in the near UV-...