The enzyme NOT involved in substrate level phosphorylation is:-
**Core Concept**
Substrate-level phosphorylation is a type of energy coupling in cellular respiration where a phosphate group is directly transferred from a high-energy compound to ADP, generating ATP. This process occurs in both glycolysis and the citric acid cycle.
**Why the Correct Answer is Right**
ATP synthase is not involved in substrate-level phosphorylation. Instead, it uses the energy from the proton gradient across the mitochondrial inner membrane to pump protons back across the membrane, driving the rotation of the stalk subunit, which in turn drives the phosphorylation of ADP to ATP through the enzyme's active site. This process is known as chemiosmosis.
**Why Each Wrong Option is Incorrect**
* **Option A:** Pyruvate kinase is involved in substrate-level phosphorylation during glycolysis. It catalyzes the transfer of a phosphate group from phosphoenolpyruvate to ADP, generating one molecule of ATP and one molecule of pyruvate.
* **Option B:** Phosphoglycerate kinase (PGK) is another enzyme involved in substrate-level phosphorylation. It catalyzes the transfer of a phosphate group from 1,3-bisphosphoglycerate to ADP, generating one molecule of ATP and one molecule of 3-phosphoglycerate.
* **Option D:** Creatine kinase is involved in substrate-level phosphorylation during the phosphocreatine kinase reaction. It catalyzes the transfer of a phosphate group from phosphocreatine to ADP, generating one molecule of ATP and one molecule of creatine.
**Clinical Pearl / High-Yield Fact**
Remember that substrate-level phosphorylation is a distinct process from oxidative phosphorylation, which relies on the energy from the electron transport chain to produce ATP through the process of chemiosmosis.
**Correct Answer: C. ATP synthase is involved in chemiosmosis, not substrate-level phosphorylation.**