The association rate constant for heme binding to globin is independent of protein structure
The association rate constant for heme binding to globin is independent of protein structure
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DOI：
10.1021/bi960371l
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发表时间：
1996-09-03
期刊：
影响因子：
2.9
通讯作者：
Olson, JS
中科院分区：
文献类型：
--
作者：
Hargrove, MS;Barrick, D;Olson, JS
速率常数CO-血红素结合到35个不同的重组脱辅基肌球蛋白和其他几个apoproteins进行了测量，努力了解血红素亲和力和缔合反应的速度的因素。令人惊讶的是，无论脱辅基蛋白的结构或对铁卟啉的总体亲和力如何，单体血红素结合的速率常数都接近1 × 10（8）M（-1）s（-1）。蛋白质之间的主要差异主要反映在辅基的解离速率上。在CO血红素与过量的脱辅基肌红蛋白反应中观察到的慢相是由于非特异性血红素-蛋白质复合物的形成，该复合物必须在血红素可以特异性地结合在血红素口袋中之前解离。一旦特定的血红素-珠蛋白复合物形成，血红素口袋迅速在卟啉周围塌陷，同时在邻近的His（93）和血红素铁原子之间形成键。抹香鲸脱辅基肌红蛋白对氯高铁血红素的总亲和力近似于1 × 10（14）M（-1）。卟啉和非极性血红素腔之间的非特异性疏水相互作用占10（5）-10（4）的因子。Fe 3+和His（93）（F8）之间的共价键形成提供了10（3）-10（4）的额外因子。与血红素口袋中保守氨基酸的特异性相互作用贡献了最终因子10（3）-10（4）。
Rate constants for CO-heme binding to 35 different recombinant apomyoglobins and several other apoproteins were measured in an effort to understand the factors governing heme affinity and the velocity of the association reaction. Surprisingly, the rate constant for the binding of monomeric heme is approximate to 1 x 10(8) M(-1) s(-1) regardless of the structure or overall affinity of the apoprotein for iron-porphyrin. Major differences between the proteins are reflected primarily in the rates of dissociation of the prosthetic group. Slow phases observed in the reaction of CO heme with excess apomyoglobin result from formation of nonspecific heme-protein complexes which must dissociate before heme can bind specifically in the heme pocket. Once the specific heme-globin complex is formed, the heme pocket rapidly collapses around the porphyrin, simultaneously forming the bond between the proximal His(93) and the heme iron atom. The overall affinity of sperm whale apomyoglobin for hemin is similar to 1 x 10(14) M(-1). Nonspecific hydrophobic interactions between the porphyrin and the apolar heme cavity account for a factor of 10(5)-10(4). Covalent bond formation between Fe3+ and His(93)(F8) provides an additional factor of 10(3)-10(4). Specific interactions with conserved amino acids in the heme pocket contribute the final factor of 10(3)-10(4).