Aspartate transcarbamoylase (ATCase) an enzyme of pyrimidine synthesys pathway, the allosteric activator of this enzyme is
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For ATCase regulation:
- CTP = Inhibitor (feedback inhibition by the pathway's end-product).
- ATP = Activator (signals abundant purines and energy).
This maintains the purine/pyrimidine balance inside the cell.
Step 1: Understanding the Concept:
Allosteric enzymes are regulated by effector molecules that bind to sites other than the enzyme's active site.
This binding induces conformational changes that either increase (activation) or decrease (inhibition) the enzyme's catalytic activity. Step 2: Detailed Explanation:
Aspartate transcarbamoylase (ATCase) catalyzes the first committed step in the pyrimidine biosynthetic pathway (the condensation of aspartate and carbamoyl phosphate to form carbamoyl aspartate).
This enzyme is a classic model for allosteric regulation:
- CTP (Cytidine Triphosphate) (B): This is the end-product of the pyrimidine pathway.
CTP acts as a feedback inhibitor by binding to the regulatory subunits of ATCase, stabilizing the low-affinity T (tense) state and reducing enzyme activity.
- ATP (Adenosine Triphosphate) (A): This is a purine nucleotide.
High levels of ATP signal that energy is abundant and that purine levels are high.
ATP binds to the same regulatory sites as CTP but stabilizes the active R (relaxed) state of the enzyme, acting as an allosteric activator.
This ensures a balanced ratio of purines to pyrimidines for DNA/RNA synthesis.
Thus, ATP is the allosteric activator of ATCase. Step 3: Final Answer:
The allosteric activator of ATCase is Adenosine triphosphate (ATP).
