section 14.1
Mitochondrial Structure and Properties
253
H3C
H,C
NADH + H +
NAD+
V
7
R
FM N
R =
— C H — '
O H O H O H
O
I I I
II
_
c —
ç — ç —
c h
2
o
— o — P — O
I I I
L
H
H
H
o
P ro tein — C y s— S-
$
r
-
-------F e -
F e -
/
Cys
P rotein
J
\
J
U
C y s
P ro tein
\
Iron-sulfur protein
co m p lex (F e
4
S4)
( s ) = acid-labile sulfur
S = cy stein e sulfur
-F e
V
Cys
P ro tein
FIGURE 14-5
Transport of reducing equivalents from NADH to FMN and structure of the iron-sulfur protein complex that mediates
electron transport from FMNH
2
to CoQ. Both FMN and the iron-sulfur centers are components of NADH-CoQ
reductase.
are organized such that iron and sulfur atoms occupy alter-
nate corners of a cube. The four iron atoms are covalently
linked via the cysteinyl sulfhydryl groups of the protein
(Figure 14-5). Complex I is inhibited by rotenone (a nat-
ural toxic plant product), amobarbital (a barbiturate), and
piericidin A (an antibiotic) (Figure 14-6). all of which act
at specific points and are useful in the study of electron
transport.
Complex II
Complex II contains succinate dehydrogenase and its
iron-sulfur centers. The complex has also been reported
to contain a specific cytochrome, cytochrome bssg.
Cy-
tochromes
are heme proteins that undergo oxidation-
reduction reactions and are differentiated on the basis
of their apoprotein structure, heme structure, and opti-
cal absorption in the visible spectrum. The mitochondrial
electron transport chain contains at least six different cy-
tochromes classified into three groups (a, b, and c). It is
usual to indicate the absorption maximum of the cc-band
of a particular cytochrome (e.g., cytochrome bsss). Succi-
nate dehydrogenase, an FAD-containing enzyme, is part of
the TCA cycle and catalyzes the trans elimination of two
hydrogens from succinate to form fumarate (Chapter 13).
FIGURE 14-6
Inhibitors of NADH-CoQ reductase: rotenone (a toxic plant product),
piericidin A (an antibiotic), and amytal (a barbiturate).
