Nucleic Acids Research, Vol 27, Issue 14 2875-2882, Copyright © 1999 by Oxford University Press
A Peracchi
The difficulties in interpreting the temperature dependence of protein
enzyme reactions are well recognized. Here, the hammerhead ribozyme
cleavage was investigated under single-turnover conditions between 0 and 60
degrees C as a model for RNA-catalyzed reactions. Under the adopted
conditions, the chemical step appears to be rate-limiting. However, the
observed rate of cleavage is affected by pre-catalytic equilibria involving
deprotonation of an essential group and binding of at least one
low-affinity Mg2+ion. Thus, the apparent entropy and enthalpy of activation
include contributions from the temperature dependence of these equilibria,
precluding a simple physical interpretation of the observed activation
parameters. Similar pre- catalytic equilibria likely contribute to the
observed activation parameters for ribozyme reactions in general. The
Arrhenius plot for the hammerhead reaction is substantially curved over the
temperature range considered, which suggests the occurrence of a
conformational change of the ribozyme ground state around physiological
temperatures.
ARTICLES
Origins of the temperature dependence of hammerhead ribozyme catalysis
Institute of Biochemical Sciences, University of Parma, 43100 Parma, Italy. peracchi@iproniv.cce.unipr.it
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