Nielsen Mette Søby, Weber Roy E
Zoophysiology, Department of Biological Sciences, University of Aarhus, DK8000 Aarhus, Denmark.
Comp Biochem Physiol A Mol Integr Physiol. 2007 Mar;146(3):429-34. doi: 10.1016/j.cbpa.2006.12.004. Epub 2006 Dec 12.
Oxygen binding to hemoglobin (Hb) depends on allosteric effectors (CO(2), lactate and protons) that may increase drastically in concentration during exercise. The effectors share common binding sites on the Hb molecules, predicting mutual interaction in their effects on Hb (de)oxygenation. We analysed the effects of lactate and CO(2), separately and in combination, on O(2) binding of purified human Hb at 37 degrees C and physiological pH and chloride values. We demonstrate pH-dependent, inhibitory interactions between lactate binding and CO(2) binding (carbamate formation); at pH 7.4, physiological CO(2) tension ( approximately 43 mm Hg) reduced lactate binding more markedly ( approximately 75%), than lactate (50 mM) inhibited carbamate formation ( approximately 25%). In contrast to previous studies on blood and Hb solutions, we moreover find that added lactate neither 'reverses' oxylabile carbamate formation (resulting in lower carbamate levels in deoxyHb than in oxyHb) nor exerts greater allosteric effects on Hb-O(2) affinity than equal increases in chloride ion concentrations.
氧气与血红蛋白（Hb）的结合取决于变构效应剂（二氧化碳、乳酸和质子），这些效应剂在运动过程中浓度可能会急剧增加。这些效应剂在Hb分子上共享共同的结合位点，预示着它们对Hb（去）氧合作用的相互影响。我们分析了乳酸和二氧化碳单独及联合作用对纯化的人Hb在37℃、生理pH值和氯化物浓度下O₂结合的影响。我们证明了乳酸结合与二氧化碳结合（氨基甲酸盐形成）之间存在pH依赖性抑制相互作用；在pH 7.4、生理二氧化碳张力（约43毫米汞柱）下，二氧化碳对乳酸结合的抑制作用（约75%）比乳酸（50 mM）对氨基甲酸盐形成的抑制作用（约25%）更为明显。与先前对血液和Hb溶液的研究不同，我们还发现添加的乳酸既不会“逆转”氧不稳定的氨基甲酸盐形成（导致脱氧Hb中的氨基甲酸盐水平低于氧合Hb），对Hb-O₂亲和力的变构效应也不会比等摩尔浓度增加的氯离子更大。
