Page 99 - The Manga Guide to Biochemistry

6. What Is CoA?

When pyruvate, which is created by glycolysis, enters into the citric acid cycle, it becomes a
substance called acetyl-CoA. But what does CoA mean?

CoA stands for coenzyme A. Its structural formula is shown below. CoA is a substance
in which two phosphates in a row are bonded to the fifth carbon of adenosine triphosphate,
and a vitamin called pantothenic acid, as well as 2-mercaptoethylamine, are also bonded.
Within the CoA, shown in the shaded part of the figure below, is the phosphopantetheine
group, which works as a “carrier” because it transports the acetyl group (aka the carbo-
hydrate chain of fatty acids). Acetyl-CoA has an acetyl group bonded at the front of this
intimidating-looking molecule.

Acetyl-CoA

OH O

H3C C ~ S CH2 CH2 N C

OP NH2

If an acetyl

group is NN

attached H H OH CH3 OO
here...

HS CH2 CH2 N C CH2 CH2 N C C C CH2 O PO PO 5´ N N
H O
CH2

O O CH3 O¯ O¯

HH

2-Mercaptoethylamine Pantothenic acid H 3´ H

O OH

Phosphopantetheine group O¯ P O

O¯

Adenosine
triphosphate

structure of CoA

Another protein that works similarly to CoA is ACP (acylcarrier protein). ACP, which we’ll
examine more thoroughly in Chapter 3, is also a “carrier.” And like CoA, it has a phosphop-
antetheine group but at a different location. The phosphopantetheine group is bonded to the
serine (a type of amino acid) of ACP rather than to adenosine triphosphate.

Since it’s called a coenzyme, CoA plays the role of assisting in chemical reactions neces-
sary in the procession of a metabolic pathway.

Photosynthesis and Respiration 85