Department of Chemistry and Biochemistry, Eastern Oregon University, La Grande, Oregon 97850, USA.
J Am Chem Soc. 2012 Jan 25;134(3):1461-3. doi: 10.1021/ja209770p. Epub 2012 Jan 9.
Cytochromes c' are pentacoordinate heme proteins with sterically hindered distal sites that bind NO and CO but do not form stable complexes with O(2). Removal of distal pocket steric hindrance via a Leu→Ala mutation yields favorable O(2) binding (K(d) ~49 nM) without apparent H-bond stabilization of the Fe-O(2) moiety, as well as an extremely high distal heme-NO affinity (K(d) ~70 fM). The native Leu residue inhibits distal coordination of diatomic ligands by decreasing k(on) as well as increasing k(off). The connection between distal steric constraints, k(off) values, and distal to proximal heme-NO conversion is discussed.
细胞色素 c' 是五配位血红素蛋白，具有空间位阻的远端部位，可与 NO 和 CO 结合，但不能与 O(2)形成稳定的配合物。通过 Leu→Ala 突变去除远端口袋位阻，有利于 O(2)结合（K(d)49 nM），而 Fe-O(2)部分没有明显的氢键稳定，同时具有极高的远端血红素-NO 亲和力（K(d)70 fM）。天然 Leu 残基通过降低 k(on)和增加 k(off)来抑制双原子配体的远端配位。讨论了远端空间位阻、k(off) 值和远端到近端血红素-NO 转换之间的关系。
