Feedback Inhibition

Feedback inhibition also known as end product inhibition refers to an important mechanism in the biosynthetic pathways involving enzymes. The synthesis of molecules such as amino acids and pyrimidines in the human body is tightly regulated and most of the steps controlled enzymatically. Usually, in feedback inhibition, the end products in biosynthetic pathways inhibit the first enzymatic step and hence controlling the synthesis of the end products themselves (Khanna, 289).

The first enzyme in the pathway which is inhibited is known as the allosteric enzyme. This mechanism takes advantage of the preexisting enzymes already in the cells to control various biosynthetic processes. An interesting example of allosteric or feedback inhibition is what happens in the biosynthesis of pyrimidine nucleotide bases which are important components of nucleic acids. The allosteric enzyme involved in the first step catalysis in the synthesis of cytidine triphosphate (CTP) is aspartate transcarbamoylase (ATCase) which catalyzes the condensation of carbamoyl phosphate and aspartate to produce orthophosphate and form N-carbamoylaspartate (Berg, Tymoczko  Stryer, 402). The CTP which is the final product of pyrimidine synthesis acts as an inhibitor to the enzyme ATCase. It is observed that the increased accumulation of CTP greatly reduces the speed (Vmax) of the enzyme ACTase (Berg, Tymoczko  Stryer, 402).

The process of feedback inhibition such as that which takes place in CTP biosynthesis is crucial in the synthesis of nucleic acids, the molecules that regulate all the life processes. In the absence of the CTP, the rate of ATCase is faster but this rate decreases when more CTP accumulates. This process is critical as it ensures that more CTP molecules are sent in the biosynthetic pathway to produce more and more pyrimidine bases. The more bases synthesized, the faster the growth process of organisms and the faster the wound healing process or DNA repair.


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