綜合11級生物化學

生物化學新陳代謝篇OxidativePhosphorylationATP

synthaseProton-motive

force:

two

components可參考電能的計算Welectricity

=

V?q++++++++++++V+電勢（Volt）點電荷（Cullen）因為實際穿越的是質(zhì)子，而不是點電荷，所以這里能量的計算以1mol質(zhì)子跨膜作為標準。We

=

V?NA

?e質(zhì)子的電量1.6e-19Avogadro

常數(shù)6.02e23=

V?FFaraday

常數(shù)96485

C/mol0.14

Volt=

13.5

kJ/mol+

-+

-+

-+

-+

-化學能的計算++++++++++++ABGAGB10?7MGB

=

Go’

+

RT

ln[H+]BGA

=

Go’

+

RT

ln[H+]A?G

=

RT

ln[H+]B

/[H+]A=

2.303RT

log10[H+]B

/[H+]A在很多情況下，線粒體內(nèi)膜兩邊的PH值差大約為1.4（matrix

高

intermembrane

space

低）log10[H+]B

/[H+]A

=

1.4?G

=

8.3

kJ/mol總能量：We

+

?G

=

21.8

kJ/molATP

synthase

(complex

V)Ball

on

a

stickF0F1Some

stick

part

γ,

ε belong

to

F1

subunitcF0

subunit:

much

of

the

stick

part10—14

c

subunits

forming

a

ringThe

ring

constitutes

the

proton

channel.1

a

subunit

binds

to

the

outside

of

the

ringF1

subunit:γ,

ε

–

the

sticky

partα,

β,

α,

β,

α,

βδF0

–

F1

connectiontwo

b

subunitsMatrixIntermembrane

spaceBlue

part: rotor

(moving)Other

part: stator

(stationary)The

reactionIt

is

intuitive

that

proton-active

force

provides

the

energy.To

verify

thisThey

use

a

special

water,

H2

18O

for

testing.Theyaddthis

H218Ointo

ADP,

Pi,

and

ATP

synthase,in

the

absence

of

proton-active

forceThey

found

18O

in

PiThis

implies

the

following

reaction

has

occurred:Where

did

ATP

comefrom?This

means

the

reaction

proceeds

evenwithout

the

proton-motive

force.ATP was

synthesized

from

ADP and

Pi

,

by

ATP

synthaseIn

totalIn

the

early

1980’s,

Paul

Boyer

at

UCLA,

proposed

the

surprisingtheory

that,

in

the

catalytic

sites

of

F1,

ATPwas

in

chemicalequilibrium

with

its

reactants,

ADP

and

phosphate.

So

theformation

of

ATP

in

the

catalytic

sites

was

essentially

withoutenergetic

cost.Nobel

Prize

in

Chemistry

(1997)The

role

of

the

proton

gradient

is

not

to

form

ATPbut

to

release

it

from

the

synthaseThree

steps:ThreeAre

there

3

components

in

structure?α,

β,

α,

β,

α,

βThree

β

subunits:

catalyze

the

above

three

tasks.The

three

β

subunits

are

the

sameBut

the

three

tasks

are

different.How

could

the

same

β

perform

different

tasks?LooseTightOpenThree

α

subunits:

Primarily

for

holding.It

is

the

γ

subunit

that

breaks

the

symmetry:each

of

the

β

subunits

is

distinct

by

virtue

ofIts

interaction

with

a

different

face

of

γ鈍角平角銳角Loose

conformation: just

binds

ADP

and

PiTightconformation: binds

with

great

avidity,

so

much

so

thatADPand

Pi converts

into

ATPOpen

conformation: allows

ATP

to

bereleasedOne

120

rotation

of

γ

counterclockwiseBlue

subunit:L

T

O

Green

subunit:O

L

T

O

L

Yellow

subunit:T

O

L

T

O

L

T

L

T

O

The

binding-change

mechanismSubunit?Subunit

cA

proton

gets

into

the

cytoplasmic

half-channel

of

the

a

Subunit

aIt

cannot

escape

if

the

Subunit

a

does

not

interact

with

othersThe

interaction

from

Subunit

c

gives

a

chance

to

the

proton.H+1.

Subunit

c

has

a

negatively

charged

residue2.

The

residue

attracts

the

protonThe

attraction

neutralizes

the

negative

chargeThis

leads

to

the

rotation

of

c

subunits (will

be

explained).5.

It

is

the

rotation

of

the

c

subunits

that

takes

away

the

protonWhy

does

the

proton

leave

the

matrix

half

channel?Diffusion?No. One

proton

does

not

diffuse

intomany

protons.Because

of

the

aspartic

acid

residue?No.

The

attraction

would

keep

the

proton.Then

what’s

the

reason?The

half

channel

must

be

polarand

positively

charged!The

charge

must

be

sufficiently

largeTo e

chemical

and

electrical

potentialThis

however

brings

about

a

problem：How

did

the

proton

load

in

the

first

place?H+It

is

the

power

of

chemical

diffusionWhy

rotate?The

essence

is

why

subunit

c

would

like

toLeave

the

cytoplasmic

half

channel?To

understand

this,

onehas

to

understandwhy

subunit

c

stabilizes

in

the

channel

beforereceiving

H+Because

one

positive,

the

other

negative+++–Because

of

H+,

subunit

c es

neutralized,and es

hydrophobicSubunit

c

leaves

to

find

other

hydrophobe:Lipid

bilayer.物以類聚Which

direction

to

rotate?Seen

from

bottom

upThat

subunit

c is

now

hydrophobic, it

wants

to

leave

the

hydrophilic subunit

aIf

the

following

direction,then

it

will

still

be

in

subunit

a,still

hydrophilic.So

must

be

the

following

direction.CounterclockwiseThe

direction

is

caused

by

asymmetryIf

symmetric,

then

no

preferred

directionSummaryDoes

α3β3

rotate

with

the

γ

unit?No.

If

otherwise,

then

α3β3

are

relatively

static

with

γ,rotation

loses

its

meaning.How

to

prevent

the

rotation

of

α3β3?The

two

b

chains

andthe

δ

subunit

fix

it

firmlyThe

number

of

c

subunits

10

—

14 is

significant2.

One

360

degree

rotation

generates

3

ATPsTake

n

=

12

as

anexample1.

One

360

degree

rotation

passes

through

12

protons3.

So

the

generation

of

one

ATP

requires4

protons.Let’s

evaluate

how

many

protons

pass

through

ATP

synthase

everydayfor

a

regular

resting

man.Recall

that

a

regular

man

generate

ATP

at

an

amount

about

his

weight.Suppose

his

weight

is

85

kg.The

molecular

weight

of

ATP

(C10H16N5O13P3) is

about

507So

everyday

the

person

generate

85000/507

=

170

mol

ATPThis

requires

passing

through

170*4

=

680

mol

of

protonsThis

is

about

680*6.02x1023

=

4x1026

of

protons

p