Final answer:
The result of downregulation of an entire metabolic pathway through allosteric modulation of the rate-limiting enzyme is called feedback inhibition. It is a regulatory mechanism where the end product of the pathway can bind to an enzyme and inhibit its activity to prevent overproduction and maintain cellular balance.
Step-by-step explanation:
When an allosterically modulated enzyme is the rate-limiting enzyme in a metabolic pathway, the entire pathway can be upregulated or downregulated by allosteric modulation. The result of downregulation of the entire pathway through this mechanism is known as feedback inhibition.
Feedback inhibition is a form of allosteric regulation where the end product of a metabolic pathway binds to the allosteric site of an enzyme, often the first enzyme in the pathway, leading to a conformational change that reduces its catalytic activity. This serves as a regulatory mechanism to control the production of substances within a cell, ensuring cellular homeostasis.
For example, if an excess of a substance in the pathway, such as substance E, accumulates, it might bind allosterically to the first enzyme in the pathway. This binding leads to an allosteric change that inhibits catalysis, which in turn slows down the entire pathway, preventing the overproduction of the end product.
Hence, the feedback inhibition mechanism allows a cell to respond dynamically to its metabolic requirements and maintain balance by controlling enzyme activities through the products of their own reactions.