The rate of electron transfer between groups
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Transcript of The rate of electron transfer between groups
The rate of electron transfer between groups– the distance between donor and acceptor of electron – the free energy change The typical electron transfer rate if groups in contact:
1013/sThe distance between electron-carrier groups: 15 A° 15 A°/1.7A° 9, decrease 10≒ 9 104/sIf no protein mediator: 15 A°/0.8A° 19, decrease 10≒ 19 10-6/s 1 day≒
0.8A° 1.7A°
e- cytochrome c Ⅲ Ⅳ
inverted region
The rate of electron transfer between groups– the distance between donor and acceptor of electron – the free energy change
Ch. 19 ?
Chemiosmotic hypothesis (1961, Mitchell P.) NADH oxidation ADP phosphorylation a covalent high-energy intermediate or an activated protein conformation proton-motive force drives the synthesis of ATP by mitochondrial ATP synthase (F1F0ATPase, complex Ⅴ)
Proton-motive force ﹙ p : the pH gradient ﹚ ﹙ pH﹚
+ the charge gradient [membrane potential ﹙ ]﹚
Testing the chemiosmotic hypothesis
Artificial membrane
Respiratory chain
ATP synthase
Proton gradient
(A purple-membrane protein,pump protons when light)
(from beef heart)
A separate system:
19.2 ATP synthesis Mitchell: chemiosmotic model, proton-motive-force
ADP + Pi + n Hp+ → ATP + H2O + n HN
+
a proton pore associated with ATP synthase
Nelson
ATP synthase mechanism: Mg2+ require
Orthophosphate
HPO42-
The role of proton gradient is to release ATP from ATP synthase but not to form ATP
ADP + Pi + ATP synthase in H218O
isotopic-exchange experiments:
enzyme-bound ATP forms readily in the absence of a proton-motive force
+ ATP synthase
ATP synthase structure
Two functional components: 1. Moving units c-ring, stalk 2. Stationary unit
matrix
(3, 3, , and )
subunits participate directly in ATP synthesis
proton channel complex c-ring (10~14 c subunits)1a, 2b, 1
Boyer PD (2000): binding-change mechanism
subunit make the 3 subunits unequivalent
Loss The conformation of binding ADP and Pi
Tight The conformation of binding ATP
Open The conformation of releasing ATP
A counterclockwise direction in subunit
Binding-change mechanism:
TL
O
Proton drive
The smallest molecular motor
Fluorescence labeled
Polyhistidine tags of N-terminal of subunit
Nicklel ions are coated on glass surface
Only cloned 33 subunits
The subunit was rotated, driven by the hydrolysis of ATP
120° increment/ATP hydrolysis
Near 100% efficiency
Components of the proton-conducting unit of ATP synthase
Two hydrophilic half-channel
Do not span the membrane
Directly about one c subunit, separately
Asp61
a pair of -helices
COO-/COOH
The site of proton entrance
Proton flow/c-ring rotation power rotation, then ATP synthesis
Arg210 in subunit a (02), Ex. 18
[H+]cyto/[H+]matrix 25
hydrophobic interaction
Proton path through the membrane
H+
C ring tightly links to
and subunits
C ring rotate
rotate
360°/3 ATP
10 c subunits/3 ATP
3.33 protons/ATP
NADH: 10 H+, 2.5 ATP
FADH2: 6 H+, 1.5 ATP Ex. 19
116 watts (joule/s) provides energy to sustain a resting person
921 earthquake
§ 18.5 Shuttles: an array of membrane-spanning transporter proteins
Glycerol 3-phosphate shuttle: electrons of cytosolic NADH from glycolysis enter mitochondrial electron
transport chain especially prominent in muscle and some insects lack lactate dehydrogenase
G3P 1,3bisP
against NADH gradient
1.5 ATP formation for
1 NADH from glycolysis
Malate-aspartate shuttle in heart and liver is readily reversible the NADH/NAD+ ratio of the cytosol is higher than that of mitochondria 2.5 ATP formation for 1 NADH from glycolysis
transamination
transamination
ATP-ADP translocase(adenine nucleotide translocase or ANT)
highly abundant in the inner mitochondrial membrane (15%) 30 kd, a single nucleotide-binding site, without Mg2+﹙Ex. 20 ﹚
ADP first entry then coupled to ATP exit, even though the transport rate of ATP is 30-fold higher than that of ADP
high energy consumed, about ¼ of the energy from e- transfer
Bongkrekic acid
Membrane potential
Proton-motive force
Ex. 22
P site
N site
atractyloside
ATP synthasome:
ATP synthase, ATP-ADP translocase, phosphate carrier(electroneutral exchange)
H2PO4-
Mitochondrial transporters
Dicarboxylate carrier
40 genes in human genome are encoded
Consumed a proton during ATP translocationOther metabolites translocated
2e- transfer less than 10H+ formation
or +5
Glucose is completely oxidized Glycolysis + 2
TCA cycle (GTP) + 2
or 32
anaerobic metabolism: 2 ATP
the rate of oxidative phosphorylation is determined by the need for ATP
Respiratory control (or acceptor control) the rate of oxidative phosphorylation is primarily regulated by ADP level
Energy charge regulation
The rate of TCA cycle is controlled by the availability of NAD+ and FAD
ATP synthasome
Uncoupling proteins (UCPs) dissipate proton flow
UCP1 (thermogenin)
Temp.
-adrenergic agonists
triacylglycerol degrade
free fatty acids liberate
Activate UCP-1
generate heat
UCP proteins: generate heat to maintain body temperature in hibernating animals, some newborn animals, and in mammals adapted to cold Brown adipose tissue (also brown fat mitochondria), which is very rich in mitochondria, is specialized for nonshivering thermogenesis (vs. white adipose tissue) regulate the body weight (obesity)[UCP2 and UCP3] increase the evaporation of odoriferous molecules, skunk cabbage
p. 533 7th line: greenish-colored cytochromes
Uncoupler disrupted the coupling of electron transport and phosphorylation – dissipated proton-motive force oxygen consumption, NADH oxidation, no ATP formation heat loss DNP and certain other acidic aromatic compounds used in some herbicides, fungicides, weight- loss drug (?)
Sites of action of inhibitors of electron transport
ferric
ferrous form of heme a3
Oligomycin
Dicyclohexylcarbodiimide
(DCCD)
prevent the influx of protons
through ATP synthase
Alternative mechanisms in plant mitochondriaAraceae: one family of stinking plants
thermogenesis
a cyanide-resistant QH2 oxidase
bypass complex III and Ⅳa rotenone insensitive NADH dehydrogenase, bypass complex Ⅰ a skunk cabbage
Nelson
Mitochondria
¤ semiautonomous organelles
¤ endosymbiotic double membrane, circular DNA, specific transcription and
translation machinery
¤ Maternally inherited
Mitochondria – diseases
a center of energy metabolism Leber hereditary optic neuropathy – NADH-Q oxidoreductase (complex )Ⅰ mutation – resulted in blindness during midlife chance fluctuation percentage the threshold of defect the accumulation of mutations effect the energy transduction, reactive oxygen species (ROS)
generation nervous system and heart are vulnerable– aging, degenerative disorders, and cancer.
Three mitochondrial cell death pathways
Apoptosis inducing factor (AIF)
Apoptotic protease activating factor-1(Apaf-1)
mtPTP
(mitochondrial permeability transition pore)
Programmed cell death
PS
Cysteine protease family
Proton gradient– a central interconvertible currency of free energy
(Mito. inner membrane)
P:O ratio:
the number of molecules of inorganic phosphate incorporated
into organic form per atom of oxygen consumed.
the number of molecules of ATP synthesized per pair of electrons
carried through electron transport.
ATP synthesis: is quantitative as phosphate uptake, conversion
of orthophosphate to organic phosphates.
Electron pairs: are quantitative as oxygen uptake.
matrix NADH: 2.5
matrix FADH2: 1.5
+ 2,4-dinitrophenol: P/O ratio from 2.5 0
Ex. 6
96C
96T 192
97T
97C
98T
98C