Key Enzymes in Glycolysis to Know for Biological Chemistry I

Glycolysis is a vital metabolic pathway that breaks down glucose to produce energy. Key enzymes like hexokinase, phosphofructokinase-1, and pyruvate kinase play crucial roles in regulating this process, ensuring efficient energy production and metabolic balance in cells.

1. Hexokinase

   • Catalyzes the phosphorylation of glucose to form glucose-6-phosphate, the first step in glycolysis.
   • Requires ATP as a phosphate donor, making it an energy-investing step.
   • Functions as a regulatory enzyme, with its activity inhibited by high levels of glucose-6-phosphate.

2. Phosphofructokinase-1 (PFK-1)

   • Acts as a key regulatory enzyme in glycolysis, converting fructose-6-phosphate to fructose-1,6-bisphosphate.
   • Requires ATP and is allosterically inhibited by ATP and citrate, while activated by AMP and fructose-2,6-bisphosphate.
   • Controls the rate of glycolysis and is often referred to as the "committed step" of the pathway.

3. Pyruvate kinase

   • Catalyzes the final step of glycolysis, converting phosphoenolpyruvate (PEP) to pyruvate while producing ATP.
   • Allosterically activated by fructose-1,6-bisphosphate, linking its activity to earlier steps in glycolysis.
   • Inhibited by ATP and alanine, ensuring that energy production is balanced with cellular needs.

4. Glucose-6-phosphate isomerase

   • Converts glucose-6-phosphate into fructose-6-phosphate, facilitating the flow of carbon through glycolysis.
   • Functions as a reversible enzyme, allowing for the interconversion of these two forms of sugar.
   • Plays a crucial role in the preparatory phase of glycolysis.

5. Aldolase

   • Catalyzes the cleavage of fructose-1,6-bisphosphate into two three-carbon sugars: dihydroxyacetone phosphate (DHAP) and glyceraldehyde-3-phosphate (G3P).
   • Essential for the continuation of glycolysis, as both products are utilized in subsequent steps.
   • Operates through a reversible reaction, allowing for metabolic flexibility.

6. Glyceraldehyde-3-phosphate dehydrogenase

   • Converts glyceraldehyde-3-phosphate into 1,3-bisphosphoglycerate, producing NADH in the process.
   • This step is crucial for energy production, as it generates a high-energy acyl phosphate compound.
   • Involves the oxidation of G3P, linking glycolysis to cellular respiration.

7. Phosphoglycerate kinase

   • Catalyzes the transfer of a phosphate group from 1,3-bisphosphoglycerate to ADP, forming ATP and 3-phosphoglycerate.
   • Represents one of the substrate-level phosphorylation steps in glycolysis, contributing to ATP production.
   • Plays a role in maintaining the energy balance within the cell.

8. Enolase

   • Converts 2-phosphoglycerate into phosphoenolpyruvate (PEP), a high-energy intermediate.
   • Involves the removal of a water molecule, making it a dehydration reaction.
   • Prepares the substrate for the final ATP-generating step of glycolysis catalyzed by pyruvate kinase.