Biochemistry 2280A Lecture Notes - Lecture 18: Semiquinone, Peptide, Electrochemical Gradient
25 Aug 2013
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Most electron carriers are embedded in the four large integral membrane protein complexes of the electron transport chain. Electron carriers differ in their affinity for electrons (from strongest reducing agent to strongest oxidant). Electrons pass from a carrier with low affinity (strong reductants like nadh) to a carrier with higher affinity (strong oxidants like o2). The electron transport chain has five types of electron carriers (in approximate order of increasing affinity for electrons): flavins, iron-sulfur centres, ubiquinone, cytochromes, and copper centres. Flavins consists of a flavin (isoalloxazine) ring that can accept two electrons (along with two protons). Examples of flavins include fadh2 and riboflavin (vitamin b2). Each iron-sulphur centre can accept one electron (per centre), in which it goes from a fe3+ to a fe2+. Two forms of iron-sulphur centres are present in nature: fe2s2 (square planar centre that accepts. 2electrons) and fe4s4 (lattice structure centre that accepts 4 electrons).
