Which of the following is true for phosphofructokinase?
**Core Concept**
Phosphofructokinase is a key regulatory enzyme in the glycolytic pathway, catalyzing the conversion of fructose-6-phosphate to fructose-1,6-bisphosphate. This step is crucial for the regulation of glucose metabolism. The enzyme is tightly regulated by various factors to ensure proper energy production.
**Why the Correct Answer is Right**
The correct answer is related to the regulation of phosphofructokinase, which is indeed a critical step in glycolysis. Phosphofructokinase is activated by AMP and inhibited by ATP and citrate, reflecting the cell's energy status. When energy levels are low (high AMP), the enzyme is activated to increase glycolysis and energy production.
**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because phosphofructokinase is not directly involved in the pentose phosphate pathway.
**Option B:** Incorrect as it does not accurately describe the primary function or regulation of phosphofructokinase.
**Option C:** Incorrect because it misrepresents the role of phosphofructokinase in glucose metabolism.
**Clinical Pearl / High-Yield Fact**
A key point to remember is that phosphofructokinase is a major regulatory enzyme in glycolysis, and its dysregulation can lead to metabolic disorders. Understanding its regulation by energy status (ATP, AMP) is crucial for comprehending glucose metabolism.
**Correct Answer:** D. Phosphofructokinase is a key regulatory enzyme in glycolysis.