Organic Chemistry

1072 CHAPTER 25 The Organic Mechanisms of the Coenzymes • Metabolism

c. What three one-carbon groups are various tetrahydrofolates capable of donating to substrates?

d. What is the function of FAD in the pyruvate dehydrogenase complex?

e. What is the function of in the pyruvate dehydrogenase complex?

f. What is the reaction necessary for proper blood clotting catalyzed by vitamin

g. What coenzymes are used for decarboxylation reactions?

h. What kinds of substrates do the decarboxylating coenzymes work on?

i. What coenzymes are used for carboxylation reactions?

j. What kinds of substrates do the carboxylating coenzymes work on?

23. Name the coenzymes that

a. allow electrons to be delocalized c. provide a good nucleophile

b. activate groups for further reaction d. provide a strong base

24. For each of the following reactions, name the enzyme that catalyzes the reaction and name the required coenzyme:

a.

b.

c.

d.

e.

f.

25.S-Adenosylmethionine (SAM) is formed from the reaction between ATP (Section 10.11) and methionine. The other product of the
reaction is triphosphate. Propose a mechanism for this reaction.

26. Five coenzymes are required by dehydrogenase, the enzyme in the citric acid cycle that converts to
    succinyl-CoA.
    a. Identify the coenzymes.
    b. Propose a mechanism for this reaction.

-ketoglutarate dehydrogenase

-ketoglutarate succinyl-CoA

CO−

O O O

−OCCH

2 CH 2 C CO 2

O O

−OCCH

2 CH 2 CSCoA +

a-ketoglutarate a-ketoglutarate

E

CH 3

CH 3 CH 2 CSCoA

O

−OCCHCSCoA

O O

− E

OCCH 2 CH 2 CCO−

O O

−OCCH

2 CCO

−

O O

O O

−OCCH

2 CH 2 CHCO

• 
  

O O

NH 3

−OCCH

2 CHCO

−

O O

+ +NH 3

+ +

E

CH 3 CCO a catabolic reaction

−

O O

CH 3 CH

OH

CO−

O

E

CH 3

−OCCHCSCoA

O O

−OCCH

2 CH 2 CSCoA

O O

E

O

SH SH

(CH 2 ) 4 CO−

O

SS

(CH 2 ) 4 CO−

E

CH 3 CSCoA ATP, Mg 2 +, HCO 3 −

O

−OCCH

2 CSCoA

O O

KH 2?

NAD+