380

chapter 18

Lipids I: Fatty Acids and Eicosanoids

® First

reduction

@ Dehydration

(D

Second

reduction

p-K etoacyl

red u ctase

NADPH + H+

^-N A D P+

Î

CH.C—

OH

I

H .C — C H -

D(-)p -Hydroxybutryl-ACP

(in successive cycles p-hydroxyacyl-ACP)

p-Hydroxyacyl

d eh y d ratase ^->h

20

H

0

HjC-

" C =

c—c—s

I

H

frans-2-Butenyl-ACP

(in su ccessive cycles a,p -u n satu rated ACP)

a , p-U nsaturated

acyl-ACP reductase

(enoyl reductase)

O

li

- C -

- NADPH + H+

-NADP+

H,C— CH,— CH,-

Butyryl-ACP

(in successive cycles acyl-ACP)

Is the acyl group16 carbons long yet?

If no

If yes

HjO

T hioester

hydrolase

Palmitic acid

(A ccepts an o th er maionyl group,

reaction

1

, an d the malonyl-

ACP initiates th e next cycle of

tw o-carbon extension.)

FIGURE 18-10

Synthesis of fatty acid. ACP = Functional unit of acyl-carrier-protein segment of fatty acid synthase. The cysteinyl-SH

group of /S-ketoacyl synthase accepts the acetyl group or the acyl group, and its catalytic site, which is adjacent to the

-SH group, catalyzes the condensation reaction.