Saturated fatty acid biosynthesis.
Saturated fatty acids play an important role in the organism. They are essential for
growth and development of the body and for normal functioning of many systems, in
prevention of atherosclerosis, regulation of the blood pressure, muscles activity and
enzymes. The lack of any of saturated fatty acid causes multiple diseases.
The first reaction in the biosynthesis of saturated fatty acids is carboxylation of
Acetyl-CoA to form Malonyl-CoA.
This reaction takes place in the presence of two enzymes, Acetyl-Coenzyme A carboxylase
alpha 1 (ACACA) , , , , , ,  and
Acetyl-Coenzyme A carboxylase beta (ACACB), , , , , , , .
Malonyl-CoA forms complex with acyl-carrier protein
Malonyl-ACP as the result of reaction catalyzed by fatty
acid synthase (FASN) , , , , . FASN
is a multifunctional protein that has 7 catalytic activities.
FASN complex consists of the enzymes cound to the acyl
carrier protein. Acetyl-ACP is formed by condensation of
Acyl-carrier protein and
Acetyl-CoA catalyzed by FASN
, , , , , , . Acetoacetyl -ACP is then synthesized
from Acetyl-ACP and Malonyl-ACP in the
reaction also catalyzed by FASN complex , , , , , , . The three recurring reactions then take place. The
first reaction is the reduction of keto group of
Acetoacetyl-ACP to alcohol group of
D-beta-Hydroxybutyryl-ACP. The second reaction is the
dehydratation of D-beta-Hydroxybutyryl-ACP resulting in
formation of Crotonyl-ACP. The third reaction is a reduction
of double bond in Crotonyl-ACP resulting in formation of
Butyryl-ACP , , , , , .
The above 3 reactions continue in a cycle. With each new turn of the cycle
FASN catalyzes attachment of a compound formed in the
previous cycle to the Malonyl-ACP complex. This results in
elongation of the saturated fatty acid chain by two carbon atoms. For example,
Butyryl-ACP from the first cycle will react with
Malonyl-ACP to form
Hexadecanoyl-ACP is formed
as a result of six consecutive cycles , , , , , , at which point
the process of biosynthesis of saturated fatty acids ends by hydrolysis of
Hexadecanoyl - ACP and release of Palmitic
acid as a final product catalyzed by FASN
, , , , , , , .
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