Effects of coenzyme analogues on the binding of p-aminobenzoyl-L-glutamate and 2,4-diaminopyrimidine to Lactobacillus casei dihydrofolate reductase.
Effects of coenzyme analogues on the binding of p-aminobenzoyl-L-glutamate and 2,4-diaminopyrimidine to Lactobacillus casei dihydrofolate reductase.
复制标题
辅酶类似物对对氨基苯甲酰基-L-谷氨酸和2,4-二氨基嘧啶与干酪乳杆菌二氢叶酸还原酶结合的影响。
作者：
B. Birdsall;A. Burgen;G. Roberts
在一系列辅酶和辅酶类似物存在下，对氨基苯甲酰基-L-谷氨酸和 2,4-二氨基嘧啶与来自干酪乳杆菌 MTX/R 的脱氢叶酸还原酶的结合已通过荧光测定法测量。这两个配体可被视为强效抑制剂甲氨蝶呤的“片段”，已被证明在没有辅酶的情况下协同结合[Birdsall, B., Burgen, A. S. V., Rodrigues de Miranda, J., & Roberts, G. C. K. (1978) Biochemistry 17, 2102]，对氨基-苯甲酰基-L-谷氨酸结合紧密58倍2,4-二氨基嘧啶存在时的效果优于不存在时的效果。在辅酶存在的情况下，这种协同作用范围为 1.8 至 428 倍。辅酶对各个结合步骤的影响范围从结合常数降低 8 倍到增加 23 倍。这些效应的结构特异性根据涉及配体诱导的构象变化的模型进行了讨论，并与上一篇论文中描述的对甲氧苄啶和甲氨蝶呤结合的影响进行了比较[Birdsall, B., Burgen, A. S. V., & Roberts, G. C. K. (1980) Biochemistry（本期四篇论文中的第一篇）]。
The binding of p-aminobenzoyl-L-glutamate and 2,4-diaminopyrimidine to dehydrofolate reductase from Lactobacillus casei MTX/R in the presence of a series of co-enzymes and coenzyme analogues has been measured fluorometrically. These two ligands, which can be regarded as "fragments" of the powerful inhibitor methotrexate, have been shown to bind cooperatively in the absence of coenzyme [Birdsall, B., Burgen, A. S. V., Rodrigues de Miranda, J., & Roberts, G. C. K. (1978) Biochemistry 17, 2102], p-amino-benzoyl-L-glutamate binding 58 times more tightly in the presence of 2,4-diaminopyrimidine than in its absence. In the presence of coenzymes, this cooperativity ranges from 1.8- to 428-fold. The effects of coenzymes on individual binding steps range from an 8-fold decrease in binding constant to a 23-fold increase. The structural specificity of these effects are discussed in terms of a model involving ligand-induced conformational changes and compared with the effects on trimethoprim and methotrexate binding described in the preceding paper [Birdsall, B., Burgen, A. S. V., & Roberts, G. C. K. (1980) Biochemistry (first paper of four in this issue)].