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Light Activates Reduction of Methotrexate by NADPH in the Ternary Complex with Escherichia coli Dihydrofolate Reductase
Author(s) -
Chen Yong Qing,
Gulotta Miriam,
Cheung H. T. Andrew,
Callender Robert
Publication year - 1999
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1111/j.1751-1097.1999.tb05309.x
Subject(s) - dihydrofolate reductase , escherichia coli , ternary complex , reduction (mathematics) , ternary operation , chemistry , methotrexate , biochemistry , enzyme , biology , computer science , mathematics , immunology , gene , geometry , programming language
— Methotrexate (MTX), a strong inhibitor of dihydrofolate reductase (DHFR), has been widely used for chemotherapy for many types of cancer as well as for juvenile rheumatoid arthritis. It mimics folate substrates and binds tightly to the active site of DHFR, perhaps in a conformation close to the transition state of the folate catalyzed reaction. Absorption, fluorescence and ultrasensitive Raman difference spectroscopies show that light‐activated MTX reacts with NADPH in the enzyme active site, producing 5,8‐dihydromethotrexate (5,8‐dihydro‐MTX) and NADP + . The reaction, which proceeds with a hydride transfer between C4 (pro‐R side) of the nicotinamide ring and N5 of the pteridine ring, is similar to that between folate and NADPH except that the hydride is transferred to C6 in this case. Hence, MTX is catalytically competent in its excited state. Most experiments were performed on the Escherichia coli enzyme, but preliminary studies show that the reaction also occurs with human DHFR.