EFFECT OF MAGNETIC-SUSCEPTIBILITY ON NUCLEAR MAGNETIC-RESONANCE SIGNALS ARISING FROM RED-CELLS - A WARNING
EFFECT OF MAGNETIC-SUSCEPTIBILITY ON NUCLEAR MAGNETIC-RESONANCE SIGNALS ARISING FROM RED-CELLS - A WARNING
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DOI：
10.1021/bi00286a020
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发表时间：
1983-01-01
期刊：
影响因子：
2.9
通讯作者：
GEORGE, RCS
中科院分区：
文献类型：
--
作者：
FABRY, ME;GEORGE, RCS
磁化率效应显然可以强烈地影响NMR谱，特别是在细胞中，并导致虚假的谱线加宽和化学位移，这将导致关于分子运动和细胞内pH和平衡常数的错误结论。研究了脱氧红细胞内外磁化率差异引起的一般现象的三个具体实例。在95 MHz的共振19 F共价结合到血红蛋白和谷胱甘肽作为三氟丙酮基化合物显然经历了大量的线增宽脱氧红细胞。在充氧溶液或充氧细胞中未观察到谱线增宽，在脱氧Hb溶液中也未观察到谱线增宽。脱氧红细胞中的宽线可以通过向悬浮介质中加入适量的顺磁性金属离子如Mn或镝来使悬浮介质的磁化率与细胞内部的磁化率相匹配而变窄。类似地，观察到2，3-二磷酸甘油酸的31 P共振的线增宽，其仅发生在脱氧红细胞中，并且具有大于1次方的场依赖性。这种谱线增宽在充氧溶液或充氧细胞中不发生，在脱氧Hb溶液中也不发生。同样，脱氧细胞中加宽的谱线可以通过匹配磁化率而变窄。因为这里报道的谱线增宽效应不依赖于细胞核、分子的化学性质或分子大小，所以它们不能归因于特定的化学相互作用或与细胞膜的相互作用。因为它们可以通过匹配内部和外部磁化率来消除，所以我们将观察到的增宽归因于磁化率差异。磁化率的差异也会导致细胞内产生的共振的化学位移的系统位移，这可能会增加或抵消由于生物化学相互作用的影响。适当的校正显然可以估计，但由于磁场梯度的存在，可能需要使用内部参考。
Magnetic susceptibility effects apparently can strongly influence NMR spectra, particularly in cells, and lead to spurious line broadening and chemical shifts which will result in false conclusions about molecular motion and intracellular pH and equilibrium constants. Three specific instances of a general phenomenon resulting from the difference in magnetic susceptibility inside and outside deoxygenated red cells were examined. At 95 MHz the resonance of 19F covalently bound to both Hb and glutathione as the trifluoroacetonyl compund apparently undergoes substantial line broadening in deoxygenated red cells. Line broadening is not observed in oxygenated solutions or oxygenated cells nor is it observed in deoxygenated Hb solutions. The broad lines in the deoxy red cell can be narrowed by matching the magnetic susceptibility of the suspending medium to that of the cell interior by adding suitable amounts of a paramagnetic metal ion such as Mn or dysprosium to the suspending medium. Similarly, line broadening of the 31P resonance of 2,3-diphosphoglyceric acid was observed which occurs only in deoxygenated red cells and has a field dependence greater than the 1st power. This line broadening does not occur in oxygenated solutions or oxygenated cells nor does it occur in deoxygenated Hb solutions. Again, the broadened lines in the deoxygenated cells can be narrowed by matching the magnetic susceptibility. Because the line-broadening effects reported here do not depend on the nucleus, the chemical nature of the molecule, or the molecular size, they cannot be attributed to specific chemical interactions or interactions with the cell membrane. Because they can be eliminated by matching the internal and external magnetic susceptibility, we attribute the observed broadening to magnetic susceptibility differences. Differences in magnetic susceptibility will also result in systematic displacement of the chemical shift of resonances arising inside the cell which may either add to or cancel effects due to biochemical interactions. The appropriate corrections apparently can be estimated but that due to the presence of magnetic field gradients use of internal references may be necessary.