La Mar G N, Budd D L, Sick H, Gersonde K
Biochim Biophys Acta. 1978 Dec 20;537(2):270-83. doi: 10.1016/0005-2795(78)90510-x.
Proton NMR studies of sperm whale and horse deoxymyoglobin have revealed that both proteins exhibit a single, well defined, pH-induced structural change. The changes in hyperfine shifts are clearly observed not only at the heme peripheral substituents, but also at the proximal histidyl imidazole, which suggest that heme-apoprotein contacts are looser in the acidic than alkaline conformations. The hyperfine shift changes are modulated by a single titratable group with a pK of approx. 5.7 in both proteins. Oxygen binding studies of sperm whale myoglobin over a range of temperature and pH showed that, while the oxygen affinity was independent of pH at 25 degrees C, it increased below pH 7 at 0 degrees C and decreased below pH 7 at 37 degrees C. Hence, sperm whale myoglobin exhibits a small acid Bohr effect which most likely arises from the characterized structural changes in the deoxy proteins. While horse myoglobin failed to exhibit a resolvable acid Bohr effect between 0 and 37 degrees C, it did show a weak alkaline Bohr effect at 25 degrees C which disappeared at lower temperatures. Since the oxygen affinity changed smoothly over several pH units, this alkaline Bohr effect can not be associated with any well defined conformational change detected by NMR.
抹香鲸和马的脱氧肌红蛋白的质子核磁共振研究表明，这两种蛋白质都表现出单一的、明确的、由pH诱导的结构变化。不仅在血红素外周取代基处，而且在近端组氨酸咪唑处都能清楚地观察到超精细位移的变化，这表明在酸性构象中血红素与载脂蛋白的接触比碱性构象中更松散。超精细位移变化由一个单一的可滴定基团调节，两种蛋白质的pK约为5.7。在一系列温度和pH条件下对抹香鲸肌红蛋白进行的氧结合研究表明，虽然在25℃时氧亲和力与pH无关，但在0℃时pH低于7时氧亲和力增加，在37℃时pH低于7时氧亲和力降低。因此，抹香鲸肌红蛋白表现出较小的酸玻尔效应，这很可能源于脱氧蛋白质中已表征的结构变化。虽然马肌红蛋白在0至37℃之间未表现出可分辨的酸玻尔效应，但在25℃时确实表现出弱的碱玻尔效应，在较低温度下消失。由于氧亲和力在几个pH单位范围内平滑变化，这种碱玻尔效应与核磁共振检测到的任何明确的构象变化无关。
