Organic Chemistry

1074 CHAPTER 25 The Organic Mechanisms of the Coenzymes • Metabolism

34. The glycine cleavage system is a group of four enzymes that together catalyze the following reaction:

Use the following information to determine the sequence of reactions involved in the glycine cleavage system:

a. The first enzyme involved in the reaction is a PLP-requiring decarboxylase.

b. The second enzyme is aminomethyltransferase. This enzyme has a lipoate coenzyme.

c. The third enzyme is an synthesizing enzyme. It catalyzes a reaction that forms as one of the

products.

d. The fourth enzyme is an FAD-requiring enzyme.

e. The cleavage system also requires

35. Nonenzyme-bound FAD is a stronger oxidizing agent than How, then, can oxidize the reduced flavoenzyme in the
    pyruvate dehydrogenase system?


36. reduces thioesters to saturated thioesters. The reaction is thought to take place by a mechanism that
    involves radicals. Propose a mechanism for this reaction.

RCH CHCSR FADH 2 RCH 2 CH 2 CSR

O O

+ + FAD

FADH 2 a,b-unsaturated

NAD+. NAD+

NAD+.

+NH

N 4

N^5 ,^10 -methylene-THF

glycine cleavage system

glycine + THF N^5 ,N^10 -methylene-THF + CO 2