Organic Chemistry

1062 CHAPTER 25 The Organic Mechanisms of the Coenzymes • Metabolism

Animals and plants cannot synthesize vitamin In fact, only a few microorgan-

isms can synthesize it. Humans must obtain all their vitamin from their diet,

particularly from meat. Because vitamin is needed in only very small amounts,

deficiencies caused by consumption of insufficient amounts of the vitamin are rare,

but have been found in vegetarians who eat no animal products. Deficiencies are most

commonly caused by an inability to absorb the vitamin in the intestine. The deficiency

causes pernicious anemia. The following are examples of enzyme-catalyzed reactions

that require coenzyme

COO− COO−

methylmalonyl-CoA

mutase

CH 3 CHCSCoA

O O

coenzyme B CH^2 CH^2 CSCoA

12

methylmalonyl-CoA succinyl-CoA

+NH 3

COO−

-methylaspartate glutamate

glutamate

mutase

CH 3 CHCHCOO−

+NH 3

COO−

CH 2 CH 2 CHCOO−

coenzyme B 12

B 12 :

B 12

B 12

B 12.

O

CH 3

CH 2

H 3 C

H 3 C

CH 2

CH 3

CH 2

H 2 N

O

CH 2

CH 2

CH 2

CH 2

C

C

O

O

P

NH 2

CH 3

CH 2 OH

O O−

O

NH 2

H 2 N

CH 2

CH 2

C

O

C

O

C

O

CH 3

CH 2

NH 2

C

O

H H

H H

O

N

NH

H

H

coenzyme B 12

H

HC

N

NH 2

CH 3

CH 3

CH 3

CH 3

CH 3

H

H

H

H

H 2 N

CH 2

CH 2

C

O

H

C

HC

OHOH

2 ́^3 ́

4 ́

5 ́

1 ́

H

OH

CH 2

C

N

N

N N

N

N

N

Co(III)

N

Dorothy Crowfoot Hodgkin
(1910–1994)was born in Egypt to
English parents. She received an
undergraduate degree from
Somerville College, Oxford
University, and earned a Ph.D. from
Cambridge University. She
determined the structures of
penicillin, insulin, and vitamin
For her work on vitamin she
received the 1964 Nobel Prize in
chemistry. She was a professor of
chemistry at Somerville, where one of
her graduate students was former
Prime Minister of England Margaret
Thatcher. Hodgkin was a founding
member of Pugwash, an organization
whose purpose was to further
communication between scientists on
both sides of the Iron Curtain.

B 12 ,

B 12.