The role of phosphate in the action of thymidine phosphorylase inhibitors: Implications for the catalytic mechanism.
The design and synthesis of 5-fluoro-6-[(2-aminoimidazol-1-yl)methyl]uracil (AIFU), a potent inhibitor of thymidine phosphorylase (TP) with K(i)-values of 11nM (ecTP) and 17nM (hTP), are described. Kinetic studies established that the type of inhibition of TP by AIFU is uncompetitive with respect to inorganic phosphate (or arsenate). The results obtained suggest that AIFU and other zwitterionic thymine analog inhibitors of TP act as transition state analogs, mimicking the anionic thymine leaving group, consistent with an S(N)2-type catalytic mechanism, and anchored by their protonated side chains to the enzyme-bound phosphate by electrostatic and H-bonding interactions.
Department of Chemistry, University at Buffalo, Buffalo, NY 14260, United States.
Harsh V
HV
Jain
Roshni
R
Rasheed
Thomas I
TI
Kalman
D002384:Catalysis; D020134:Catalytic Domain; D004791:Enzyme Inhibitors / Q000737:chemistry*; D006860:Hydrogen Bonding; D007700:Kinetics; D010710:Phosphates / Q000737:chemistry*; D011485:Protein Binding; D055672:Static Electricity; D013939:Thymidine Phosphorylase / Q000037:antagonists & inhibitors* / Q000378:metabolism; D013941:Thymine / Q000031:analogs & derivatives / Q000737:chemistry / Q000494:pharmacology
D004791:Enzyme Inhibitors; D010710:Phosphates; D013939:Thymidine Phosphorylase; D013941:Thymine