Gray Harry B, Winkler Jay R
Beckman Institute, California Institute of Technology 1200 E California Boulevard Pasadena CA 19925 USA
Chem Sci. 2021 Sep 27;12(42):13988-14003. doi: 10.1039/d1sc04286f. eCollection 2021 Nov 3.
Electrons can tunnel through proteins in microseconds with a modest release of free energy over distances in the 15 to 20 Å range. To span greater distances, or to move faster, multiple charge transfers (hops) are required. When one of the reactants is a strong oxidant, it is convenient to consider the movement of a positively charged "hole" in a direction opposite to that of the electron. Hole hopping along chains of tryptophan (Trp) and tyrosine (Tyr) residues is a critical function in several metalloenzymes that generate high-potential intermediates by reactions with O or HO, or by activation with visible light. Examination of the protein structural database revealed that Tyr/Trp chains are common protein structural elements, particularly among enzymes that react with O and HO. In many cases these chains may serve a protective role in metalloenzymes by deactivating high-potential reactive intermediates formed in uncoupled catalytic turnover.
电子能够在微秒内穿过蛋白质，在15至20埃的距离上适度释放自由能。为了跨越更大的距离或更快地移动，则需要多次电荷转移（跳跃）。当其中一种反应物是强氧化剂时，考虑带正电的“空穴”在与电子相反的方向上移动会很方便。沿着色氨酸（Trp）和酪氨酸（Tyr）残基链的空穴跳跃是几种金属酶中的关键功能，这些金属酶通过与O或HO反应，或通过可见光激活来生成高电位中间体。对蛋白质结构数据库的研究表明，Tyr/Trp链是常见的蛋白质结构元件，特别是在与O和HO反应的酶中。在许多情况下，这些链可能通过使在非耦合催化周转中形成的高电位反应中间体失活，在金属酶中起到保护作用。
