Chapter 23, Problem 36P

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

$\text{glycine}+\text{THF}\underset{\to }{\text{glycine}\text{cleavage}\text{system}}{N}^5,N^{10}-\text{methylene}-\text{THF}+{\text{CO}}_{\text{2}}$

Use the following information to determine the sequence of reactions carried out by the glycine cleavage system:

a. The first enzyme is a PLP-requiring decarboxylase.

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

c. The third enzyme synthesizes N⁵_,N¹⁰-methylene-THF and also forms ⁺NH₄.

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

e. The cleavage system also requires NAD⁺.