Rong Q, Espanol M, Mota de Freitas D, Geraldes C F
Department of Chemistry, Loyola University of Chicago, Illinois 60626.
Biochemistry. 1993 Dec 14;32(49):13490-8. doi: 10.1021/bi00212a014.
We used 7Li NMR spin-lattice (T1) and spin-spin (T2) relaxation time measurements to investigate the binding of Li+ in human red blood cell (RBC) suspensions. In RBCs containing 1.4 mM Li+, the intracellular 7Li NMR T2 relaxation value (0.30 +/- 0.03 s) was much smaller than the corresponding T1 value (6.0 +/- 0.1 s), yielding a ratio of T1 to T2 of 20. For 1.5 mM LiCl solutions whose viscosities were adjusted to 5 cP with glycerol, the values of the T1/T2 ratios were as follows: 49 for unsealed RBC membrane (2.0 mg of protein/mL); 4.4 for spectrin (1.9 mg/mL); 1.5 for 5.4 mM 2,3-bisphosphoglycerate (BPG); 2.2 for 2.7 mM carbonmonoxyhemoglobin (COHb); 1.6 for 2.0 mM ATP; and 1.2 for a 50/50% (v/v) glycerol-water mixture. Intracellular viscosity and the electric field gradients experienced by Li+ when traversing the spectrin-actin network therefore are not responsible for the large values of the T1/T2 ratios observed in Li(+)-loaded RBCs. We conclude that the RBC membrane is the major Li+ binding site in Li(+)-loaded RBCs (Kb = 215 +/- 36 M-1) and that the binding of Li+ to COHb, BPG, spectrin-actin, or ATP is weak. Partially relaxed 7Li NMR spectra of Li(+)-containing RBC membrane suspensions indicated the presence of two relaxation components, one broad and one narrow.(ABSTRACT TRUNCATED AT 250 WORDS)
我们利用7Li核磁共振自旋晶格（T1）和自旋 - 自旋（T2）弛豫时间测量来研究锂离子在人红细胞（RBC）悬液中的结合情况。在含有1.4 mM Li+的红细胞中，细胞内7Li核磁共振T2弛豫值（0.30±0.03秒）远小于相应的T1值（6.0±0.1秒），T1与T2的比值为20。对于用甘油将粘度调至5厘泊的1.5 mM LiCl溶液，T1/T2比值如下：未密封的红细胞膜（2.0毫克蛋白质/毫升）为49；血影蛋白（1.9毫克/毫升）为4.4；5.4 mM 2,3 - 二磷酸甘油酸（BPG）为1.5；2.7 mM一氧化碳血红蛋白（COHb）为2.2；2.0 mM三磷酸腺苷（ATP）为1.6；50/50%（v/v）甘油 - 水混合物为1.2。因此，细胞内粘度以及锂离子穿过血影蛋白 - 肌动蛋白网络时所经历的电场梯度并非导致在负载Li+的红细胞中观察到的高T1/T2比值的原因。我们得出结论，红细胞膜是负载Li+的红细胞中主要的Li+结合位点（结合常数Kb = 215±36 M-1），并且Li+与COHb、BPG、血影蛋白 - 肌动蛋白或ATP的结合较弱。含Li+的红细胞膜悬液的部分弛豫7Li核磁共振谱表明存在两种弛豫成分——一种宽峰和一种窄峰。（摘要截选至250字）
