Abstract
The peptidyl transferase reaction on the ribosome is catalyzed by RNA. Pre-steady-state kinetic studies using Escherichia coli ribosomes suggest that catalysis (>10 5-fold overall acceleration) is, to a large part, a result of substrate positioning, in agreement with crystal structures of large ribosomal subunits with bound substrate or product analogs. The rate of peptide bond formation is inhibited approximately 100-fold by protonation of a single ribosomal group with a p K a of 7.5, indicating general acid-base catalysis and/or a pH-dependent conformational change within the active site. According to the kinetics of mutant ribosomes, these effects may be attributed to a candidate catalytic base (A2451) suggested by the crystal structure.
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