Activation of R235A mutant orotidine 5'-monophosphate decarboxylase by the guanidinium cation: effective molarity of the cationic side chain of Arg-235.
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) x OMP complex, with a K(d) of 50 mM, to form the 9-fold more reactive ternary E(mut) x OMP x Gua(+) complex. The "effective molarity" of the cationic side chain of Arg-235 at the wild-type enzyme is calculated to be 160 M.
Barnett
Shonoi A
SA
Department of Chemistry, University at Buffalo, SUNY, Buffalo, New York 14260-3000, USA.
Amyes
Tina L
TL
Wood
B McKay
BM
Gerlt
John A
JA
Richard
John P
JP
D000409:Alanine / Q000235:genetics; D019943:Amino Acid Substitution / Q000235:genetics*; D001120:Arginine / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D002384:Catalysis; D002414:Cations, Monovalent / Q000737:chemistry*; D004789:Enzyme Activation / Q000235:genetics; D004795:Enzyme Stability / Q000235:genetics; D005656:Fungal Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D019791:Guanidine / Q000737:chemistry*; D009964:Orotidine-5'-Phosphate Decarboxylase / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D011485:Protein Binding / Q000235:genetics; D021122:Protein Subunits / Q000737:chemistry / Q000235:genetics / Q000378:metabolism
D002414:Cations, Monovalent; D005656:Fungal Proteins; D021122:Protein Subunits; D001120:Arginine; D009964:Orotidine-5'-Phosphate Decarboxylase; D019791:Guanidine; D000409:Alanine