3-Phosphoglycerate phosphorylation

The remaining steps in the glycolytic pathway prepare for synthesis of the second ATP equivalent. This begins with the phosphoglycerate mutase reaction (Eigure 19.23), in which the phosphoryl group of 3-phosphoglycerate is moved... 

FIGURE 19.24 A mechanism for the phosphoglycerate mutase reaction in rabbit muscle and in yeast. Zelda Rose of the Institute for Cancer Research in Philadelphia showed that the enzyme requires a small amount of 2,3-BPG to phosphorylate the histidine residue before the mechanism can proceed. Prior to her work, the role of the phosphohistidine in this mechanism was not understood. 

FIGURE 19.25 The phosphoglycerate mutase of wheat germ catalyzes an intramolecn-lar phosphoryl transfer. 

A different mechanism operates in the wheat germ enzyme. 2,3-Bisphosphoglycerate is not a cofactor. Instead, the enzyme carries out intra-molecular phosphoryl group transfer (Figure 19.25). The C-3 phosphate is transferred to an active-site residue and then to the C-2 position of the original substrate molecule to form the product, 2-phosphoglycerate. 

Like all anhydrides (Section 21.5), the mixed carboxylic-phosphoric anhydride is a reactive substrate in nucleophilic acyl (or phosphoryl) substitution reactions. Reaction of 1,3-bisphosphoglycerate with ADR occurs in step 7 by substitution on phosphorus, resulting in transfer of a phosphate group to ADP and giving ATP plus 3-phosphoglycerate. The process is catalyzed by phospho-gjvcerate kinase and requires Mg2+ as cofactor. Together, steps 6 and 7 accomplish the oxidation of an aldehyde to a carboxylic acid. 

A monomeric enzyme, PGK transfers the acylated phosphoryl group from 1,3- bisphosphoglycerate to ADP, thus forming 3-phosphoglycerate and ATP. The enzyme uses a metal ion as a cofactor, namely Mg2+ [65]. The PGK enzyme from T. bruceihas been overexpressed in E. coli [66]. Human PGK is not... 

The enzyme phosphoglycerate mutase catalyzes a reversible shift of the phosphoryl group between C-2 and C-3 of glycerate Mg2+ is essential for this reaction ... 

In the second glycolytic reaction that generates a compound with high phosphoryl group transfer potential, enolase promotes reversible removal of a molecule of water from 2-phosphoglycerate to yield phosphoenolpyruvate (PEP) ... 

Figure 15-6 Generation of ATP coupled to oxidation of an aldehyde to a carboxylic acid. The most important known example of this sequence is the oxidation of glyceraldehyde 3-phosphate to 3-phosphoglycerate (Fig. 10-3, steps a and b). Other important sequences for "substrate-level" phosphorylation are shown in Eq. 14-23 and in Fig. 15-16.

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