蚯蚓血红蛋白与氧相互作用的动力学

Kinetics of the hemerythrin-oxygen interaction.

作者信息

de Waal D J, Wilkins R G

出版信息

J Biol Chem. 1976 Apr 25;251(8):2339-43.

Abstract

The kinetics of the reaction of Golfingia gouldii hemerythrin with O2 have been studied by stopped flow spectrophotometry. For the second order oxygenation process, k1 = 7.4 X 10(6) M-1 s-1, deltaH1++ = 8.2 kcal-mol-1 and deltaS1++ = +1 e.u. at 25 degrees, pH 8.2, and I = 0.015 M. The rate constant is unchanged when protein concentration is varied from 3 to 25 muM, the ionic strength is increased to 0.07 M, and the pH moved to 6.8. The deoxygenation of oxyhemerythrin is studied with stopped flow by scavenging liberated O2 with S2O4(2-). For the first order dissociation, k-1 = 51 s-1, deltaH-1++ = 20.6 kcal-mol-1 and deltaS-1++ = +19 e.u. at 25 degrees, pH 8.2, and I = 0.015 M. The value of k-1 is independent of [protein] = 50 to 200 muM, [S2O4(2-)] = 5 to 100 mM I = 0.015 to 0.30 M and pH 6.8 to 9.0. Using myoglobin instead of S2O4(2-) as scavenger gives similar results. Combination of activation parameters for the oxygenation and deoxygenation processes gives K1 = 1.5 X 10(5) M-1, deltaH = -12.4 kcal-mol-1, and deltaS = -18 e.u., values in good agreement with independent thermodynamic data. Perchlorate ion (0.05 M) enhances k-1 about 3-fold and hardly effects k1. There is no sign of other than a single reaction in either direction, and octameric hemerythrin apparently behaves kinetically as eight single units.

摘要

利用停流分光光度法研究了古氏蛰龙介血赤蛋白与O₂反应的动力学。对于二级氧化过程，在25℃、pH 8.2、离子强度I = 0.015 M条件下，k1 = 7.4×10⁶ M⁻¹ s⁻¹，ΔH1⁺⁺ = 8.2 kcal·mol⁻¹，ΔS1⁺⁺ = +1 e.u.。当蛋白质浓度在3至25 μM范围内变化、离子强度增加到0.07 M以及pH值变为6.8时，速率常数不变。通过用S₂O₄²⁻清除释放出的O₂，利用停流法研究了氧合血赤蛋白的脱氧过程。对于一级解离，在25℃、pH 8.2、离子强度I = 0.015 M条件下，k⁻¹ = 51 s⁻¹，ΔH⁻¹⁺⁺ = 20.6 kcal·mol⁻¹，ΔS⁻¹⁺⁺ = +19 e.u.。k⁻¹的值与蛋白质浓度[蛋白质] = 50至200 μM、[S₂O₄²⁻] = 5至100 mM、离子强度I = 0.015至0.30 M以及pH值6.8至9.0无关。用肌红蛋白代替S₂O₄²⁻作为清除剂可得到类似结果。氧化和脱氧过程的活化参数相结合得到K1 = 1.5×10⁵ M⁻¹，ΔH = -12.4 kcal·mol⁻¹，ΔS = -18 e.u.，这些值与独立的热力学数据吻合良好。高氯酸根离子（0.05 M）使k⁻¹增大约3倍，而对k1几乎没有影响。在两个方向上均未显示出除单一反应之外的迹象，并且八聚体血赤蛋白在动力学上显然表现为八个单一组分。