Studies on cobalt myoglobins and hemoglobins. I. Preparation and optical properties of myoglobins and hemoglobins containing cobalt proto-, meso-, and deuteroporphyrins and thermodynamic characterization of their reversible oxygenation.
Studies on cobalt myoglobins and hemoglobins. I. Preparation and optical properties of myoglobins and hemoglobins containing cobalt proto-, meso-, and deuteroporphyrins and thermodynamic characterization of their reversible oxygenation.
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钴肌红蛋白和血红蛋白的研究。
DOI：
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发表时间：
1974
影响因子：
4.8
通讯作者：
G. Woodrow
中科院分区：
文献类型：
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作者：
T. Yonetani;H. Yamamoto;G. Woodrow
人工肌红蛋白和含钴卟啉原、中位和后位（原、中位和后位- comb和- cohb）的血红蛋白在吡啶存在下，通过将抹香鲸的无肌红蛋白和人血液中的apo血红蛋白与钴卟啉进行厌氧重组，可重复制备。这些CoMb和CoHb每个血红素结合位点含有一个钴卟啉，并且能够可逆氧化，证实了Hoffman和Petering （(1970) Proc. Nat. Acad. Sci.）的原始观察。《美国法典》第67卷，637-643页)。建立了它们的光吸收特性和消光系数。通过Imai等人（1970）的自动氧合测量。Biophys。Acta 200,189 - 196)，得到了半饱和时torr中氧的分压（p0.5）和半饱和时Hill's系数(n)的值。CoMb的p0.5值比相应的含铁肌红蛋白（FeMb）的p0.5值大50 ~ 100倍，在存在和不存在六磷酸肌醇的情况下，CoMb的p0.5值在pH 6.5 ~ 8.0的范围内是恒定的。CoHb的p0.5值比相应的含铁血红蛋白（FeHb）大10 ~ 25倍。proto-、meso-和deutero-CoHb的碱性玻尔效应（∂log p0.5/∂pH）分别为0.5、0.3和0.3。在0.1 m磷酸缓冲液中加入500µm六磷酸肌醇，pH 7.0， CoHb的p0.5值增加3倍。卟啉侧链的化学修饰对含铁和含钴氧载体的氧亲和性的影响已被发现在很大程度上取决于载脂蛋白的性质和温度。观察到的p0.5序列为：CoMb和FeMb在25°以上为原- g中- g重卟啉，CoMb和FeMb在20°以下为原- g中- g重卟啉，CoHb和FeHb在3-30°处为原- g重- g重卟啉。这些p0.5序列的变化表明，侧链修饰对氧亲和的影响是立体化学的，而不是电子的。原卟啉IX在CoHb中具有最小的氧亲和力和最大的协同性。对含铁和含钴氧载体氧参数的热化学比较表明，金属取代对氧亲和力的影响主要是焓的，而载脂蛋白结合对钴卟啉氧亲和力的影响主要是熵的。
Abstract Artificial myoglobins and hemoglobins containing cobaltous proto-, meso-, and deuteroporphyrins (proto-, meso-, and deutero-CoMb and -CoHb) have been prepared reproducibly by an anaerobic recombination of apomyoglobin from sperm whale and apohemoglobin from human blood with cobaltous porphyrins in the presence of pyridine. These CoMb and CoHb contain one cobalt porphyrin per heme binding site and are capable of reversible oxygenation, confirming the original observation of Hoffman and Petering ((1970) Proc. Nat. Acad. Sci. U. S. A. 67, 637–643). Their optical absorption characteristics and extinction coefficients have been established. By means of the automatic oxygenation measurements of Imai et al. ((1970) Biochim. Biophys. Acta 200, 189–196), the following values have been obtained for the partial pressure of oxygen in torr at half-saturation (p0.5) and Hill's coefficient (n) at half-saturation. The p0.5 values of CoMb are 50 to 100 times larger than those of the corresponding iron-containing myoglobins (FeMb) and are constant in a range from pH 6.5 to 8.0 in both the presence and absence of inositol hexaphosphate. The p0.5 values of CoHb are 10 to 25 times larger than the corresponding iron-containing hemoglobins (FeHb). The alkaline Bohr effects (∂ log p0.5/∂ pH) for proto-, meso-, and deutero-CoHb are 0.5, 0.3, and 0.3, respectively. The p0.5 value of CoHb increases 3-fold upon addition of 500 µm inositol hexaphosphate in 0.1 m phosphate buffer, pH 7.0. The effect of chemical modifications of porphyrin side chains on the oxygen affinity of iron- and cobalt-containing oxygen carriers has been found to vary considerably depending on the nature of apoprotein and temperature. The observed sequence of p0.5 is: proto- g meso- g deuteroporphyrins for CoMb and FeMb above 25°, meso- g proto- g deuteroporphyrins for cobaltous porphyrin dimethylesters, CoMb, and FeMb below 20°, and proto- g deutero- g mesoporphyrins for CoHb and FeHb at 3–30°. These variations of the p0.5 sequence suggest that the effect of side chain modifications on the oxygen affinity is stereochemical rather than electronic. Protoporphyrin IX is required for a minimal oxygen affinity and a maximal cooperativity in CoHb. Thermochemical comparison of oxygenation parameters of iron- and cobalt-containing oxygen carriers indicates that the effect of the metal substitution on the oxygen affinity is primarily enthalpic, whereas the effect of the apoprotein binding on the oxygen affinity of cobaltous porphyrins is essentially entropic.