a. Hexokinase - Used only in glycolysis
b. Glucose-6-phosphatase - Used only in gluconeogenesis
c. PEP Carboxykinase, Aldolase - Used in glycolysis and gluconeogenesis
Hexokinase is an enzyme that plays a crucial role in glycolysis by catalyzing the conversion of glucose to glucose-6-phosphate. This reaction occurs early in the glycolytic pathway and represents the initial step in trapping glucose within the cell. Hexokinase is not involved in gluconeogenesis, as it catalyzes an irreversible step that contributes to the commitment of glucose to glycolysis.
Glucose-6-phosphatase, on the other hand, is an enzyme exclusive to gluconeogenesis. It functions in the endoplasmic reticulum of liver cells and catalyzes the hydrolysis of glucose-6-phosphate to release free glucose. This step is essential for maintaining blood glucose levels during fasting periods.
PEP Carboxykinase and Aldolase are enzymes that participate in both glycolysis and gluconeogenesis. PEP Carboxykinase catalyzes the conversion of oxaloacetate to phosphoenolpyruvate (PEP) in gluconeogenesis and catalyzes the reverse reaction in glycolysis. Aldolase is involved in the cleavage of fructose-1,6-bisphosphate into glyceraldehyde-3-phosphate and dihydroxyacetone phosphate in glycolysis, and it catalyzes the reverse reaction in gluconeogenesis.
These distinctions highlight the intricate regulation and interplay of enzymes in glycolysis and gluconeogenesis, allowing organisms to finely tune their metabolic pathways based on the availability of nutrients and energy requirements.