Which of the following enzyme does not catalyse the irreversible step in glycolysis?
Correct Answer: Phosphoglycero kinase
Description: Step 1 of Glycolysis - i. Glucose is phosphorylated to glucose-6- phosphate. ii. The enzyme is hexokinase (HK),which splits the ATP into ADP, and the Pi is added on to the glucose. The energy released by the hydrolysis of ATP is utilized for the forward reaction. iii. Hexokinase is a key glycolytic enzyme. Hexokinase catalyses a regulatory step in glycolysis that is irreversible. But this irreversibility is circumvented by another enzyme glucose-6-phosphatase (see gluconeogenesis). Step 3 of Glycolysis - i. Fructose-6-phosphate is fuher phosphorylated to fructose1,6-bisphosphate. The enzyme is phosphofructokinase. ii. PFK is an allosteric, inducible, regulatory enzyme. It is an impoant key enzyme of this pathway. This is again an activation process, the energy being derived by hydrolysis of yet another molecule of ATP. This irreversible step is the rate limiting reaction in glycolysis. However, during gluconeogenesis, this step is circumvented by fructose-1,6-bisphosphatase. Step 9 of Glycolysis - i. Phosphoenol pyruvate (PEP) is dephosphorylated to pyruvate, by pyruvate kinase. First PEP is made into a transient intermediary of enol pyruvate; which is spontaneously isomerized into keto pyruvate, the stable form of pyruvate. ii. One mole of ATP is generated during this reaction. This is again an example of substrate level phosphorylation. iii. The pyruvate kinase is a key glycolytic enzyme. This step is irreversible. REF: DM VASUDEVAN TEXTBOOK OF BIOCHEMISTRY, EIGHTH EDITION,PG.NO.,129,131.
Category:
Biochemistry
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