3-Phosphoglycerate formation

Most of the enzymes mediating the reactions of the Calvin cycle also participate in either glycolysis (Chapter 19) or the pentose phosphate pathway (Chapter 23). The aim of the Calvin scheme is to account for hexose formation from 3-phosphoglycerate. In the course of this metabolic sequence, the NADPH and ATP produced in the light reactions are consumed, as indicated earlier in Equation (22.3). 

One excellent example of a Emax-type allosteric enzyme is Escherichia coli phosphoglycerate dehydrogenase (PGDH), a tetramer of identical subunits that catalyzes the formation of D-3-phosphohydroxypyruvate from D-3-phosphoglycerate in a reaction that uses NAD+ as a redox cofactor. This regulatory enzyme is allosteri-cally controlled by serine. All available information suggests that the effects on the for substrate are minor... 

FIGURE 10.6 Protein enzyme phosphoglycerate kinase involved in the formation of adenosine-5 -triphosphate (ATP) from adenosine-5 -diphosphate (ADP). 

The major pathway for the formation of serine is the same in all organisms (Fig. 22-12). In the first step, the hydroxyl group of 3-phosphoglycerate is oxidized by a... 

Formation of pyruvate. The conversion of glucose to pyruvate requires ten enzymes (Fig. 17-7), and the sequence can be divided into four stages preparation for chain cleavage (reactions 1-3), cleavage and equilibration of triose phosphates (reactions 4 and 5), oxidative generation of ATP (reactions 6 and 7), and conversion of 3-phosphoglycerate to pyruvate (reactions 8-10). 

Any of these three compounds can serve as the precursor for synthesis of other organic materials. A first stage in biosynthesis consists of those reactions by which 3-phosphoglycerate or PEP arise, whether it be from C02, formate, acetate, lipids, or polysaccharides. 

Another aspect of chloroplast metabolism is synthesis of starch. Formation of ADP-glucose from glucose 1-phosphate is induced by 3-phosphoglycerate, a "feed-ahead" type of regulation (Fig. 23-36). Although fructose 2,6-bisphosphate is absent from chloroplasts, it has an important regulatory function in the cytoplasm of plants as it does in animals.425 430 In the plant cytosol triose phosphates from the chloroplasts are converted to fructose 6-P, glucose 6-P, UDP-... 

The mixed anhydride of phosphoric acid and glyceric acid then is used to convert ADP to ATP and form 3-phosphoglycerate. Thereafter the sequence differs from that in photosynthesis. The next few steps accomplish the formation of pyruvate by transfer of the phosphoryi group from C3 to C2 followed by dehydration to phosphoenolpyruvate. Phosphoenolpyruvate is an effective phosphorylating agent that converts ADP to ATP and forms pyruvate ... 

Carreras, J., F. Climent, R. Bartrons, and G. Pons. 1982. Effect of vanadate on the formation and stability of the phosphoenzyme forms of 2,3-bisphosphoglycerate-dependent phosphoglycerate mutase and of phosphoglucomutase. Biochim. Biophysic. Acta 705 238-242. 

---