Chm 635-3

Chm 635-3 - 1 11.4 Free-Energy Changes in Glycolysis Actual...

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Unformatted text preview: 1 11.4 Free-Energy Changes in Glycolysis Actual free-energy changes ( G) large only for: #1 (hexokinase) #3 (phosphofructokinase) #10 (pyruvate kinase) These steps are metabolically irreversible, and these enzymes are regulated G for all other steps are close to zero (they are near-equilibrium in cells) 2 Regulation of Glycolysis Regulation of Glycolysis 1. Hexokinases: inhibited by excess glucose 6-phosphate . 2. PFK1: allosterically inhibited by ATP and citrate and activated by AMP and F-2,6- bisphosphate. AMP and fructose 2,6- bis phosphate (F2,6BP) relieve the inhibition of PFK-1 by ATP 3. Pyruvate Kinase: regulated by allosteric modulators and by phosphorylation . When ATP is needed, glycolysis is activated. When ATP levels are sufficient, glycolysis activity decreases 3 PFK-1 Regulation: ATP and AMP AMP relieves ATP inhibition of PFK-1 http://www.wiley.com/legacy/college/fob/quiz/quiz14/14-22.html PFK-1 Regulation: Fructose 2,6-bisphosphate (F2,6BP) F2,6BP is a highly potent activator of PFK1 4 PFK-1 Regulation: Fructose 2,6-bisphosphate (F2,6BP) F2,6BP is synthesized by PFK2, which is a bifunctional enzyme. PFK2 is regulated by hormone glucagon, which causes its phosphorylation 5 Pyruvate Kinase (PK): Allosteric regulation by F1,6BP and ATP Four PK isozymes exist in mammalian tissues PK is allosterically activated by F1,6BP, and inhibited by ATP Glucagon stimulates protein kinase A which phosphorylates PK converting it to a less active form (liver and intestinal cells) 6 Pyruvate Kinase (PK): Hormonal regulation by phosphorylation Initial velocity curves of pyruvate kinase 7 The Pasteur Effect Under anaerobic conditions the conversion of glucose to pyruvate is much higher than under aerobic conditions (yeast cells produce more ethanol and muscle cells accumulate lactate) The Pasteur Effect is the slowing of glycolysis in the presence of oxygen More ATP is produced under aerobic conditions than under anaerobic conditions, therefore less glucose is consumed aerobically Rate of anaerobic glycolysis is 100 times faster than that of oxidative phosphorylation....
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Chm 635-3 - 1 11.4 Free-Energy Changes in Glycolysis Actual...

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