ATP levels would fall at first, decreasing the inhibition of PFK and increasing the rate of ATP production.
Feedback inhibition is difficult to reverse.
Feedback inhibition involves enzymatic actions in a reaction being stopped as a result of the formation of a product.
Feedback inhibition is easy to reverse as long as the products are removed or absent. Feedback inhibition can work almost instantaneously and regulates the flow through biosynthetic pathways.
Feedback inhibition is also known as a feedback system for controlling enzyme activity and the enzyme acting early in a reaction pathway is inhibited by a later product of that pathway.
Feedback inhibition takes place when an enzyme acting early in a reaction pathway is inhibited by a late product of that pathway.
In this type of regulation, the product of the process actively inhibits the previous formation chain to stabilize the compound so that its level doesn't rise more than necessary.
Let's take for example the Hypothalamic-pituitary-adrenal axis.
Upon receiving a stimulus (for example stress), the hypothalamic cells secrete corticotropin-releasing hormone (CRH). This hormone is transported through the portal blood vessels to the anterior pituitary where it stimulates the secretion of stored adrenocorticotropic hormone (ACTH).
The ACTH travels through blood to the adrenal cortex of the adrenal gland where it stimulates the biosynthesis of glucocorticoids (mainly cortisol).
The hormone produced in the adrenal cortex will negatively feedback to inhibit both the hypothalamus and the pituitary gland. This reduces the secretion of CRH and the release of ACTH.
CRH ← Inhib. ← ↑
Anterior Pituitary ↑
ACTH ← Inhib. ← ↑
Adrenal cortex ↑
Cortisol → → ↑
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So your A leads to production of B which leads to production of C which leads to production of D
In feedback inhibition (or a negative feedback loop), the final product of a pathway (in this case, D) will usually inhibit or stop the first step in that pathway. So in this instance, D would do something to stop A-->B from occurring. It could bind A or the enzyme that makes that step occur.
Basically, the end product somehow stops one of the earliest steps in the pathway