Zang L H, Laughlin M R, Rothman D L, Shulman R G
Department of Molecular Biophysics and Biochemistry, School of Medicine, Yale University, New Haven, Connecticut 06510.
Biochemistry. 1990 Jul 24;29(29):6815-20. doi: 10.1021/bi00481a009.
The field dependence of relaxation times of the C-1 carbon of glycogen was studied in vitro by natural-abundance 13C NMR. T1 is strongly field dependent, while T2 does not change significantly with magnetic field. T1 and T2 were also measured for rat hepatic glycogen enriched with [1-13C]glucose in vivo at 4.7 T, and similar relaxation times were observed as those obtained in vitro at the same field. The in vitro values of T1 were 65 +/- 5 ms at 2.1 T, 142 +/- 10 ms at 4.7 T, and 300 +/- 10 ms at 8.4 T, while T2 values were 6.7 +/- 1 ms at 2.1 T, 9.4 +/- 1 ms at 4.7 T, and 9.5 +/- 1 ms at 8.4 T. Calculations based on the rigid-rotor nearest-neighbor model give qualitatively good agreement with the T1 field dependence with a best-fit correlation time of 6.4 X 10(-9) s, which is significantly smaller than tau M, the estimated overall correlation time for the glycogen molecule (ca. 10(-5) s). A more accurate fit of T1 data using a modified Lipari and Szabo approach indicates that internal fast motions dominate the T1 relaxation in glycogen. On the other hand, the T2 relaxation is dominated by the overall correlation time tau M while the internal motions are almost but not completely unrestricted.
通过天然丰度的13C NMR体外研究了糖原C-1碳弛豫时间的场依赖性。T1强烈依赖于场，而T2随磁场变化不显著。还在4.7 T下对体内富含[1-13C]葡萄糖的大鼠肝糖原测量了T1和T2，观察到的弛豫时间与在相同场强下体外获得的相似。T1的体外值在2.1 T时为65±5 ms，在4.7 T时为142±10 ms，在8.4 T时为300±10 ms，而T2值在2.1 T时为6.7±1 ms，在4.7 T时为9.4±1 ms，在8.4 T时为9.5±1 ms。基于刚性转子最近邻模型的计算与T1场依赖性在定性上有很好的一致性，最佳拟合相关时间为6.4×10(-9) s，这明显小于糖原分子的估计整体相关时间tau M（约10(-5) s）。使用改进的Lipari和Szabo方法对T1数据进行更精确的拟合表明，内部快速运动主导了糖原中的T1弛豫。另一方面，T2弛豫由整体相关时间tau M主导，而内部运动几乎但并非完全不受限制。
