Dihydrofolate reductase from the pathogenic fungus Pneumocystis carinii: catalytic properties and interaction with antifolates.
Dihydrofolate reductase from the pathogenic fungus Pneumocystis carinii: catalytic properties and interaction with antifolates.
复制标题
来自致病真菌卡氏肺囊虫的二氢叶酸还原酶：催化特性以及与抗叶酸剂的相互作用。
DOI：
10.1006/abbi.1993.1453
复制
发表时间：
1993
影响因子：
3.9
通讯作者：
Blakley,RL
中科院分区：
文献类型：
--
作者：
Margosiak,SA;Appleman,JR;Santi,DV;Blakley,RL
Dihydrofolate reductase (DHFR) from the fungusPneumocystis carinii(pcDHFR), a target for antifolate inhibitors, has been compared with host enzyme, human DHFR (hDHFR), and with DHFR fromEscherichia coli. Among the results of the considerable structural differences between pcDHFR and the other two enzymes is a much higher turnover number (kcat, 136 s−1) for pcDHFR. This is due to rapid hydride transfer from NADPH to dihydrofolate (rate constant 402 s−1), very rapid dissociation of NADP from the product complex (rate constant,koff, > 1000 s−1), and after NADPH binding, rapid dissociation of tetrahydrofolate (koff, 216 s−1). Cycling of pcDHFR is almost exclusively by this pathway. The highkcatcontributes to a highKmfor NADPH (9 μM) and an unusually highKmfor dihydrofolate (2.5 μM). Nevertheless, the efficiency of pcDHFR is greater than DHFR fromE. coliand about 25% that of hDHFR. Of seven clinically relevant inhibitors investigated, only one (trimethoprim) had a slightly lowerKifor pcDHFR than for hDHFR. The therapeutic value of trimethoprim-sulfa treatment ofP. cariniiinfections indicates that other factors play an important role, but the results are consistent with the frequency of complications due to toxicity of trimethoprim.
