Question

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What rqgulatory enzyme of glycolysis is skipped during fructose metabolism? hexokinase phosphoglucose isomerase phosphofructokinase pyruvate kinase

Answer 1

(c) phosphofructokinase

Phosphofructokinase is the most important control element in the mammalian glycolytic pathway (Figure 16.16). High levels of ATP allosterically inhibit the enzyme in the liver (a 340-kd tetramer), thus lowering its affinity for fructose 6-phosphate. A high concentration of ATP converts the hyperbolic binding curve of fructose 6-phosphate into a sigmoidal one (Figure 16.17). ATP elicits this effect by binding to a specific regulatory site that is distinct from the catalytic site.AMP reverses the inhibitory action of ATP, and so the activity of the enzyme increases when the ATP/AMP ratio is lowered. In other words, glycolysis is stimulated as the energy charge falls. A fall in pH also inhibits phosphofructokinase activity. The inhibition of phosphofructokinase by H+ prevents excessive formation of lactic acid (Section 16.1.9) and a precipitous drop in blood pH (acidosis).

This enyme has no role in fructolysis.