Bicout D J, Field M J, Gouet P, Jouve H M
Laboratoire de Dynamique Moléculaire, Institut de Biologie Structurale Jean-Pierre Ebel, Grenoble, France.
Biochim Biophys Acta. 1995 Sep 27;1252(1):172-6. doi: 10.1016/0167-4838(95)00123-c.
Catalase-bound NADPH both prevents and reverses the accumulation of compound II, an inactive form of catalase that is generated from the normal active intermediate form (compound I) when catalase is exposed to a steady flow of hydrogen peroxide. The mechanism for the regeneration reaction is unknown although NADPH could act either as a one-electron or a two-electron donor. Recently, a reaction scheme has been proposed in which the formation of compound II from compound I generates a neighboring radical species within the protein. NADPH would then donate two electrons, one to compound II for reduction of the iron and the other to the protein free radical. In this paper, we report calculations to find the dominant electron tunneling pathways between NADPH and the heme iron in the catalase from the peroxide-resistant mutant of Proteus mirabilis. Two major tunneling pathways are found which fuse together on Ser-196. It is suggested that the sequence Gly-Ser of the loop that divides the beta 5-strand is the key element for shielding a radical amino acid.
与过氧化氢酶结合的NADPH既能防止又能逆转化合物II的积累，化合物II是过氧化氢酶的一种无活性形式，当过氧化氢酶暴露于稳定的过氧化氢流中时，它由正常的活性中间形式（化合物I）产生。尽管NADPH可以作为单电子或双电子供体，但再生反应的机制尚不清楚。最近，有人提出了一种反应方案，其中化合物I形成化合物II会在蛋白质内产生相邻的自由基物种。然后，NADPH将提供两个电子，一个给化合物II用于铁的还原，另一个给蛋白质自由基。在本文中，我们报告了相关计算，以找到奇异变形杆菌耐过氧化物突变体过氧化氢酶中NADPH与血红素铁之间的主要电子隧穿途径。发现了两条主要的隧穿途径，它们在Ser-196处合并。有人认为，分隔β5链的环的Gly-Ser序列是屏蔽自由基氨基酸的关键元素。
