**Core Concept**
Phosphofructokinase (PFK) and fructose 1,6-bisphosphatase (FBPase-1) are key regulatory enzymes in the glycolytic and gluconeogenic pathways, respectively. Phosphofructokinase catalyzes the conversion of fructose-6-phosphate to fructose-1,6-bisphosphate in glycolysis, while fructose 1,6-bisphosphatase catalyzes the reverse reaction in gluconeogenesis. The regulation of these enzymes by fructose 2,6-bisphosphate is a critical mechanism for controlling the balance between glycolysis and gluconeogenesis.

**Why the Correct Answer is Right**
Fructose 2,6-bisphosphate is a potent allosteric regulator of PFK and FBPase-1. It activates PFK by increasing its affinity for fructose-6-phosphate, thereby promoting glycolysis. Conversely, it inhibits FBPase-1 by decreasing its activity, thereby suppressing gluconeogenesis. This regulation is mediated through the binding of fructose 2,6-bisphosphate to specific sites on the enzymes, which alters their conformation and activity. The phospho-dephosphorylation of these enzymes by fructose 2,6-bisphosphate is a critical step in this regulatory process.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is not relevant to the regulation of PFK and FBPase-1 by fructose 2,6-bisphosphate.
* **Option B:** This option is incorrect because the regulation of PFK and FBPase-1 by fructose 2,6-bisphosphate is not mediated by a direct interaction with the enzymes' active sites.
* **Option C:** This option is incorrect because the regulation of PFK and FBPase-1 by fructose 2,6-bisphosphate is not dependent on the presence of insulin or glucagon.

**Clinical Pearl / High-Yield Fact**
Fructose 2,6-bisphosphate is a key regulator of glucose metabolism, and its levels are tightly controlled by feedback mechanisms to prevent excessive glycolysis or gluconeogenesis. This regulation is critical for maintaining normal blood glucose levels and preventing metabolic disorders.

**Correct Answer:** C. Insulin and glucagon.