Iqbal M P, Rothenberg S P, da Costa M
Department of Biochemistry, Aga Khan University Medical College, Karachi, Pakistan.
Biochem Med Metab Biol. 1991 Oct;46(2):196-207. doi: 10.1016/0885-4505(91)90067-u.
Two species of DHFR were identified in wild-type L1210 murine leukemia cells by analysis of the kinetics of the binding of MTX and dissociation of the MTX-enzyme complex at pH 5.0 and pH 7.2. The two forms of DHFR were also distinguished by immunoinhibition of the binding of MTX and the catalytic reduction of FH2 to FH4 using an antiserum raised to the purified high affinity form of DHFR. The Ka for the binding of MTX by the low affinity form of the enzyme is 4.5 x 10(7) M-1, substantially lower than the reported Ka for the binding of this drug by the high affinity enzyme. The low affinity form of the enzyme catalyzed the reduction of FH2 to FH4 at a rate slower than the high affinity form of DHFR.
通过在pH 5.0和pH 7.2条件下分析甲氨蝶呤（MTX）的结合动力学以及MTX-酶复合物的解离情况，在野生型L1210小鼠白血病细胞中鉴定出了两种二氢叶酸还原酶（DHFR）。使用针对纯化的高亲和力形式DHFR产生的抗血清，通过对MTX结合的免疫抑制以及将二氢叶酸（FH2）催化还原为四氢叶酸（FH4），也区分出了这两种形式的DHFR。该酶的低亲和力形式结合MTX的解离常数（Ka）为4.5×10⁷ M⁻¹，显著低于报道的该药物与高亲和力酶结合的Ka值。该酶的低亲和力形式催化FH2还原为FH4的速率比高亲和力形式的DHFR慢。
