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CASE FILES: BIOCHEMISTRY
single iron atom chelated by four cysteine sulfurs; others contain two
iron atoms chelated through four cysteine sulfurs and two inorganic sulfurs;
yet others contain four iron atoms chelated by four cysteine sulfurs and
four inorganic sulfurs.
Coenzyme Q (ubiquinone): A two electron accepting quinone that can
accept and transfer one electron at a time allowing it to exist in a semi-
quinone state as well as the fully oxidized quinone or fully reduced dihy-
droxy state. It is bound to multiple isoprenoid units (ubiquinone has ten
units), allowing it to bind to the membrane.
Flavin mononucleotide (FMN): An isoalloxazine ring bound to ribosyl
monophosphate in an N-glycosidic bond. FMN can accept two electrons
or donate one at a time to another electron acceptor.
Flavin adenine dinucleotide (FAD): An isoalloxazine ring bound to ribo-
syl monophosphate in an N-glycosidic bond which is attached to adeno-
sine monophosphate. Like FMN, FAD can accept or donate two
electrons one at a time to another electron acceptor.
D ISC U SSIO N
The electron transport chain (ETC) or electron transport system (ETS)
shown in Figure 16-1 is located on the inner membrane of the mitochon-
drion and is responsible for the harnessing of free energy released as elec-
trons travel from more reduced (more negative reduction potential, E ) to
more oxidized (more positive
E'g)
carriers to drive the phosphorylation of
ADP to ATP. Complex I accepts a pair of electrons from NADH
(E'0 =
-0.32 V)
Figure 16-1. Schematic diagram of electron transport chain ATP synthase and
ATP/ADP translocase.
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