Trematode hemoglobins show exceptionally high oxygen affinity
Trematode hemoglobins show exceptionally high oxygen affinity
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DOI：
10.1016/s0006-3495(98)77587-3
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发表时间：
1998-08-01
影响因子：
3.4
通讯作者：
Marden, MC
中科院分区：
文献类型：
--
作者：
Kiger, L;Rashid, AK;Marden, MC
本文研究了从克氏胃吸虫（Gc）、副复口吸虫（Pe）、棘口吸虫（Ee）、水牛寄生蠕虫（布法罗）和高唇等节吸虫（Ih）中分离的血红蛋白（Hb）与配体的结合。氧和一氧化碳结合的动力学显示出非常快的缔合速率。然而，在25摄氏度下，氧气可以在毫秒的时间尺度上从人类Hb中被置换，而从吸虫Hb中解离氧气可能需要几秒到超过20秒（对于Hb Pe）。然而，一氧化碳解离比其他单体血红蛋白或肌红蛋白更快。吸虫血红蛋白也显示出降低的自氧化速率;氧形式不容易被铁氰化钾氧化，表明只有脱氧形式与这种氧化剂快速反应。与大多数脊椎动物血红蛋白不同，吸虫在E7位有一个酪氨酸残基，而不是通常的远端组氨酸。对于也显示出高氧亲和力的蛔虫血红蛋白，吸虫在B10位有一个酪氨酸;两个与氧分子相连的氢键被认为是导致非常高的氧亲和力的原因。吸虫血红蛋白显示高结合率和非常低的解离率的组合，导致有史以来观察到的一些最高的氧亲和力。
Ligand binding studies were made with hemoglobin (Hb) isolated from trematode species Gastrothylax crumenifer (Gc), Paramphistomum epiclitum (Pe), Explanatum explanatum (Ee), parasitic worms of water buffalo Bubalus bubalis, and Isoparorchis hypselobagri (Ih) parasitic in the catfish Wallago attu. The kinetics of oxygen and carbon monoxide binding show very fast association rates. Whereas oxygen can be displaced on a millisecond time scale from human Hb at 25 degrees C, the dissociation of oxygen from trematode Hb may require a few seconds to over 20 s (for Hb Pe), Carbon monoxide dissociation is faster, however, than for other monomeric hemoglobins or myoglobins. Trematode hemoglobins also show a reduced rate of autoxidation; the oxy form is not readily oxidized by potassium ferricyanide, indicating that only the deoxy form reacts rapidly with this oxidizing agent. Unlike most vertebrate Hbs, the trematodes have a tyrosine residue at position E7 instead of the usual distal histidine, As for Hb Ascaris, which also displays a high oxygen affinity, the trematodes have a tyrosine in position B10; two H-bonds to the oxygen molecule are thought to be responsible for the very high oxygen affinity. The trematode hemoglobins display a combination of high association rates and very low dissociation rates, resulting in some of the highest oxygen affinities ever observed.