TY - JOUR
T1 - Conformational change rate-limits GTP hydrolysis
T2 - The mechanism of the ATP sulfurylase-GTPase
AU - Wei, Jiang
AU - Leyh, Thomas S.
PY - 1998/12/8
Y1 - 1998/12/8
N2 - The fluorescent GTP analogues 3'-O-(N-methylanthraniloyl)-2'- deoxyguanosine 5'-(β,γ-imidotriphosphate) (mGMPPNP) and 3'-O-(N- methylanthraniloyl)-2'-deoxy-GTP (mGTP) were used to demonstrate that an enzyme isomerization precedes and rate-limits β,γ-bond cleavage in the catalytic cycle of the ATP sulfurylase-GTPase, from E. coli K-12. The binding of mGMPPNP to the E-AMP·PP(i) complex of ATP sulfurylase is biphasic, indicating that an isomerization occurs in the binding reaction. The isomerization mechanism was assigned based on the results of the enzyme concentration dependence of the observed rate constants, k(obs), for both phases of the binding reaction, and sequential-mixing, nucleotide release experiments. The isomerization occurs after, and is driven by, the addition of mGMPPNP. Values were determined for each of the rate constants associated with the two-step kinetic model used in the interpretation of the results. A comparison of the enzyme concentration dependence of k(obs) for the hydrolysis and binding reactions reveals that the rate constants for the corresponding steps of these two reactions are extremely similar. The virtually identical rate constants for isomerization and β,γ-bond scission strongly suggest that isomerization rate-limits bond breaking. The implications of these finding for GTPase/target interactions and the mechanism of energetic linkage in the ATP sulfurylase system are discussed.
AB - The fluorescent GTP analogues 3'-O-(N-methylanthraniloyl)-2'- deoxyguanosine 5'-(β,γ-imidotriphosphate) (mGMPPNP) and 3'-O-(N- methylanthraniloyl)-2'-deoxy-GTP (mGTP) were used to demonstrate that an enzyme isomerization precedes and rate-limits β,γ-bond cleavage in the catalytic cycle of the ATP sulfurylase-GTPase, from E. coli K-12. The binding of mGMPPNP to the E-AMP·PP(i) complex of ATP sulfurylase is biphasic, indicating that an isomerization occurs in the binding reaction. The isomerization mechanism was assigned based on the results of the enzyme concentration dependence of the observed rate constants, k(obs), for both phases of the binding reaction, and sequential-mixing, nucleotide release experiments. The isomerization occurs after, and is driven by, the addition of mGMPPNP. Values were determined for each of the rate constants associated with the two-step kinetic model used in the interpretation of the results. A comparison of the enzyme concentration dependence of k(obs) for the hydrolysis and binding reactions reveals that the rate constants for the corresponding steps of these two reactions are extremely similar. The virtually identical rate constants for isomerization and β,γ-bond scission strongly suggest that isomerization rate-limits bond breaking. The implications of these finding for GTPase/target interactions and the mechanism of energetic linkage in the ATP sulfurylase system are discussed.
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U2 - 10.1021/bi9817461
DO - 10.1021/bi9817461
M3 - Article
C2 - 9860829
AN - SCOPUS:0032497924
SN - 0006-2960
VL - 37
SP - 17163
EP - 17169
JO - Biochemistry
JF - Biochemistry
IS - 49
ER -