Kinetics of NO and O2 binding to a maleimide poly(ethylene glycol)-conjugated human haemoglobin.
Kinetics of NO and O2 binding to a maleimide poly(ethylene glycol)-conjugated human haemoglobin.
复制标题
DOI：
10.1042/bj20040156
复制
发表时间：
2004-08
期刊：
影响因子：
--
通讯作者：
K. Vandegriff;A. Bellelli;M. Samaja;A. Malavalli;M. Brunori;R. Winslow
中科院分区：
文献类型：
--
作者：
K. Vandegriff;A. Bellelli;M. Samaja;A. Malavalli;M. Brunori;R. Winslow
大多数无细胞血红蛋白观察到的高血压效应被认为是NO清除的结果。然而，新开发的PEG [聚乙二醇]缀合血红蛋白MalPEG-Hb [马来酰亚胺活化的PEG缀合血红蛋白]是非高血压的，具有独特的物理化学性质：高O2亲和力、低协同性和大分子半径。因此，将MalPEG-Hb与未修饰的无细胞HbA（无基质人血红蛋白）的配体结合性质进行比较是有意义的。脱氧和oxyMalPEG-Hb和HbA的NO结合率被发现是相同的。这些结果证实，对于具有高分子半径和低p50（血红蛋白被O2半饱和时的pO 2）的类似修饰血红蛋白，高血压和NO之间缺乏相关性[Rohlfs，Bruner，Chiu，冈萨雷斯，冈萨雷斯，Magde，Magde，Vandegriff和温斯洛（1998）生物化学杂志273，12128-12134]。的R-状态O2协会的动力学常数也是相同的两个血红蛋白。然而，尽管MalPEG-Hb的p50约为0.001。HbA的一半，在相对高的pO 2（150 Torr）下测量的双相O2解离速率高2倍，导致MalPEG-Hb的R-状态平衡缔合常数比HbA低2倍。因此，MalPEG-Hb的O2亲和力仅在低于MalPEG-Hb和HbA的O2平衡曲线交点的pO 2值时较高。总之，本研究发现类似的速率的NO结合HbA和MalPEG-Hb，消除了可能性，即缺乏血管活性的MalPEG-Hb仅仅是降低分子反应性与NO。或者，独特的O2结合特性与低p50和协同性表明，“R-状态”构象的MalPEG-Hb是在一个更T-状态的配置和限制构象变化。
The hypertensive effect observed with most cell-free haemoglobins has been proposed to result from NO scavenging. However, a newly developed PEG [poly(ethylene glycol)]-conjugated haemoglobin, MalPEG-Hb [maleimide-activated PEG-conjugated haemoglobin], is non-hypertensive with unique physicochemical properties: high O2 affinity, low co-operativity and large molecular radius. It is therefore of interest to compare the ligand-binding properties of MalPEG-Hb with unmodified cell-free HbA (stroma-free human haemoglobin). NO association rates for deoxy and oxyMalPEG-Hb and HbA were found to be identical. These results confirm the lack of correlation between hypertension and NO for a similar modified haemoglobin with high molecular radius and low p50 (pO2 at which haemoglobin is half-saturated with O2) [Rohlfs, Bruner, Chiu, Gonzales, Gonzales, Magde, Magde, Vandegriff and Winslow (1998) J. Biol. Chem. 273, 12128-12134]. The R-state O2 association kinetic constants were also the same for the two haemoglobins. However, even though the p50 of MalPEG-Hb is approx. half of that of HbA, the biphasic O2 dissociation rates measured at relatively high pO2 (150 Torr) were 2-fold higher, giving rise to a 2-fold lower R-state equilibrium association constant for MalPEG-Hb compared with HbA. Thus the O2 affinity of MalPEG-Hb is higher only at pO2 values lower than the intersection point of the O2 equilibrium curves for MalPEG-Hb and HbA. In summary, the present studies found similar rates of NO binding to HbA and MalPEG-Hb, eliminating the possibility that the lack of vasoactivity of MalPEG-Hb is simply the result of reduced molecular reactivity with NO. Alternatively, the unique O2-binding characteristics with low p50 and co-operativity suggest that the 'R-state' conformation of MalPEG-Hb is in a more T-state configuration and restricted from conformational change.