The Simultaneous Oxidation and Phosphorylation of Glyceraldehyde 3-Phosphate Forms a Highly

Multiple Choice

The simultaneous oxidation and phosphorylation of glyceraldehyde 3-phosphate forms a highly reactive covalent thioester bond between a cysteine side chain (reactive group ?SH) on the enzyme (glyceraldehyde 3-phosphate dehydrogenase) and the oxidized intermediate (see the arrow in Figure 13-23A) .If the enzyme had a serine (reactive group ?OH) instead of a cysteine at this position, which could form only a much lower energy bond to the oxidized substrate (see the arrow in Figure 13-23B) , how might this new enzyme act? (A)


(B)

Figure 13-23

A) It would oxidize the substrate and phosphorylate it without releasing it.
B) It would oxidize the substrate but not release it.
C) It would phosphorylate the substrate on the 2 position instead of the 1 position.
D) It would behave just like the normal enzyme.