Glycolysis enzymes

FIGURE 14.2 The breakdown of glucose by glycolysis provides a prime example of a metabolic pathway. Ten enzymes mediate the reactions of glycolysis. Enzyme A, fructose 1,6, hiphos-phate aldolase, catalyzes the C—C bondbreaking reaction in this pathway. 

All of the glycolysis reactions ranging from phosphoenolpyruvate to fructose 1,6-bisphosphate are reversible, and the phosphoenolpyruvate molecules formed are consumed for producing fructose 1,6-bisphosphate by making use of the same glycolysis enzymes. 

Fructose 6-phosphate is phosphorylated by ATP, forming fructose 1,6-bis-phosphate and ADP. This reaction is the first committed step in glycolysis. -Enzyme phosphofructokinase 1 (PFK1)... 

Citrate acts allosterically to stimulate polymerization of acetyl-CoA carboxylase (regulatory enzyme for fatty acid biosynthesis) and inhibits the glycolysis enzyme, phosphofructokinase. 

Next step of glycolysis Enzymes of glycolysis Glycolysis overview... 

The enzyme is regulated allosterically and the of the reaction (-14.2 kJ/mol) is sufficiently negative to make it essentially irreversible in vivo. Consequently gluconeogenesis uses the enzyme fructose-1,6-bisphosphatase to hydrolyze F1,6BP to F6P. PFK is,thus, one of the glycolysis enzymes that is not used in gluconeogenesis. 

See also Regulation of Gluconeogenesis, Fructose-2,6-Bisphosphate in Gluconeogenesis Regulation, Gluconeogenesis Enzymes, Glycolysis Enzymes, AMP... 

Figure 5.25 Analytes used for the discrimination study intermediates, cofactors, and direct allosteric controls (+ positive, negative) in the pathway of glycolysis. Enzyme names are given in italics.

Aldolase and phosphofructokinase (glycolysis enzymes) have high activities at the early stages after imbibition, and then they decline. 

Activities of the pentose phosphate pathway enzymes glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase increase as activities of the glycolysis enzymes decline. 

Figure 10.3-23. Metabolic model of glycolysis and tbe pentose phosphate pathway in E. coli. Squares Indicate enzyme activities circles indicate regulatory effects,...

This cleavage is a retro aldol reaction It is the reverse of the process by which d fruc tose 1 6 diphosphate would be formed by aldol addition of the enolate of dihydroxy acetone phosphate to d glyceraldehyde 3 phosphate The enzyme aldolase catalyzes both the aldol addition of the two components and m glycolysis the retro aldol cleavage of D fructose 1 6 diphosphate... 

Further steps m glycolysis use the d glyceraldehyde 3 phosphate formed m the aldolase catalyzed cleavage reaction as a substrate Its coproduct dihydroxyacetone phosphate is not wasted however The enzyme triose phosphate isomerase converts dihydroxyacetone phosphate to d glyceraldehyde 3 phosphate which enters the glycol ysis pathway for further transformations... 

The glycolytic pathway described in this chapter begins with the breakdown of glucose, but other sugars, both simple and complex, can enter the cycle if they can be converted by appropriate enzymes to one of the intermediates of glycolysis. Figure 19.32 shows the mechanisms by which several simple metabolites can enter the glycolytic pathway. Fructose, for example, which is pro-... 

For each of the following reactions, name the enzyme that carries out this reaction in glycolysis and write a suitable mechanism for the reaction. 

Pyruvate carboxylase is the most important of the anaplerotie reactions. It exists in the mitochondria of animal cells but not in plants, and it provides a direct link between glycolysis and the TCA cycle. The enzyme is tetrameric and contains covalently bound biotin and an Mg site on each subunit. (It is examined in greater detail in our discussion of gluconeogenesis in Chapter 23.) Pyruvate carboxylase has an absolute allosteric requirement for acetyl-CoA. Thus, when acetyl-CoA levels exceed the oxaloacetate supply, allosteric activation of pyruvate carboxylase by acetyl-CoA raises oxaloacetate levels, so that the excess acetyl-CoA can enter the TCA cycle. 

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). 

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