Kiger L, Rashid A K, Griffon N, Haque M, Moens L, Gibson Q H, Poyart C, Marden M C
INSERM U473, 94276 Le Kremlin Bicêtre Cedex, France.
Biophys J. 1998 Aug;75(2):990-8. doi: 10.1016/S0006-3495(98)77587-3.
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.
对从水牛（Bubalus bubalis）体内寄生的吸虫类皱襞腹袋吸虫（Gastrothylax crumenifer，Gc）、表膜双口吸虫（Paramphistomum epiclitum，Pe）、展形阔盘吸虫（Explanatum explanatum，Ee）以及鲶鱼（Wallago attu）体内寄生的异双盘吸虫（Isoparorchis hypselobagri，Ih）中分离出的血红蛋白（Hb）进行了配体结合研究。氧气和一氧化碳结合动力学显示结合速率非常快。在25摄氏度时，氧气可在毫秒时间尺度上从人血红蛋白中被置换出来，而吸虫血红蛋白中氧气的解离可能需要几秒到20多秒（对于血红蛋白Pe）。然而，一氧化碳的解离比其他单体血红蛋白或肌红蛋白更快。吸虫血红蛋白的自氧化速率也有所降低；氧合形式不易被铁氰化钾氧化，这表明只有脱氧形式能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位置有一个酪氨酸残基，而不是通常的远端组氨酸。至于同样表现出高氧亲和力的蛔虫血红蛋白，吸虫在B10位置有一个酪氨酸；与氧分子的两个氢键被认为是其极高氧亲和力的原因。吸虫血红蛋白表现出高结合速率和极低解离速率的组合，导致观察到一些有史以来最高的氧亲和力。
