Activation of R235A Mutant Orotidine 5 '-Monophosphate Decarboxylase by the Guanidinium Cation: Effective Molarity of the Cationic Side Chain of Arg-235

作者：Barnett Shonoi A; Amyes Tina L; Wood B McKay; Gerlt John A; Richard John P^*

来源：Biochemistry, 2010, 49(5): 824-826.

DOI：10.1021/bi902174q

The R235A mutation at yeast orotidine 5'-monophosphate decarboxylase (OMPDC results in a 1300-fold increase in K(m) and a 14-fold decrease in k(cat) for decarboxylation of orotidine 5'-monophosphate, corresponding to a 5.8 kcal/mol destabilization of the transition state. There is strong activation of this mutant enzyme by added guanidinium cation (Gua(+)): 1 M Gua(+) stabilizes the transition state by ca. 3 kcal/mol. This stabilization is due to the binding of Gua(+) to the binary E(mut).OMP complex, witha K(d) of 50 mM, to form the 9-fold more reactive ternary E(mut).OMP.Gua(+) complex. The "effective molarity" of the cationic side chain of Arg-235 at the wild-type enzyme is calculated to be 160 M.

• 出版日期2010-2-9