J. Biol. Chem., Vol. 255, Issue 17, 8229-8233, 09, 1980
Structure of metal x nucleotide complex in the creatine kinase reaction. A study with diastereomeric phosphorothioate analogs of adenosine di- and triphosphate
PM Burgers and F Eckstein
The diastereomers of adenosine 5'-O-(1-thiotriphosphate) (ATP alpha S) and
adenosine 5'-O-(2-thiotriphosphate) (ATP beta S) were tested as substrates
for creatine kinase in the presence of different activating divalent metal
cations. In the presence of Mg2+, the Rp diastereomers of both ATP alpha S
and ATP beta S are the preferred substrates, whereas in the presence of
Cd2+, the Sp diastereomers are preferred. In the reverse reaction the Rp
isomer of ADP alpha S is the better substrate in the presence of Mg2+ while
the Sp isomer is preferred in the presence of Cd2+. In the presence of
Mg2+, only the Rp isomer of ATP beta S is synthesized from prochiral ADP
beta S while the Sp isomer is synthesized predominantly in the presence of
Cd2+. In the presence of Ca2+, Mn2+, and Co2+, loss of substrate
specificity is observed. These results are explained on the basis of the
observation that Mg2+ prefers to coordinate to oxygen and Cd2+ to sulfur in
these phosphorothioate analogs (Jaffe, E. K., and Cohn, M. (1978) J. Biol.
Chem. 253, 4823-4825). Thus, the metal ion appears to be bound to both the
alpha- and beta-phosphates at some stage of the reaction. The
interpretation is that the substrate binds as the lambda, beta, gamma-
bidentate MgATP chelate. It can then undergo either nucleophilic
substitution at the gamma-phosphorus followed by migration of the metal to
yield the alpha, beta MgADP complex or metal migration followed by
subsequent phosphoryl transfer. The product of the reaction is delta,
alpha, beta-bidentate MgADP. The different reaction routes are discussed.
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