Collman J P, Brauman J I, Doxsee K M, Halbert T R, Suslick K S
Proc Natl Acad Sci U S A. 1978 Feb;75(2):564-8. doi: 10.1073/pnas.75.2.564.
O2 binding to a series of ferrous and cobaltous "picket fence" porphyrins is reported. N-Methylimidazole and covalently attached imidazoles gives O2 binding to ferrous porphyrins with deltaH degrees =-16.2 kcal/mol (-67.7 kJ/mol) and deltaS degrees =-40 eu (standard state, 1 atmosphere O2). Similar studies with cobaltous porphyrins yield deltaH degrees =- 12.8 kcal/mol (-53.5 kJ/mol) and deltaS degrees =- 39 eu. These values match well those of myoglobin and isolated subunits of hemoglobin and their cobalt reconstituted analogues. 1,2-Dimethylimidazole has been successfully used to mimic the presumed restraint of T state hemoglobin. In direct analogy to the decreased cooperativity shown by cobalt-substituted hemoglobin, model cobalt porphyrins show a smaller decrease in O2 affinity than the analogous iron porphyrins when the axial base is hindered. Thermodynamic data are presented. The molecular mechanism of cooperativity in hemoglobin is discussed.
报道了氧气与一系列亚铁和亚钴“栅栏”卟啉的结合情况。N - 甲基咪唑和共价连接的咪唑使氧气与亚铁卟啉结合，其ΔH° = - 16.2千卡/摩尔（- 67.7千焦/摩尔），ΔS° = - 40熵单位（标准状态，1个大气压氧气）。对亚钴卟啉进行的类似研究得出ΔH° = - 12.8千卡/摩尔（- 53.5千焦/摩尔），ΔS° = - 39熵单位。这些数值与肌红蛋白以及血红蛋白的分离亚基及其钴重构类似物的数值非常吻合。1,2 - 二甲基咪唑已成功用于模拟推测的T态血红蛋白的限制作用。与钴取代血红蛋白所显示的协同性降低直接类似，当轴向碱基受阻时，模型钴卟啉的氧气亲和力下降幅度比类似的铁卟啉小。给出了热力学数据，并讨论了血红蛋白协同性的分子机制。
