**Core Concept**
The Insulin: Glucagon ratio is a critical determinant of glucose metabolism, with an imbalance leading to various metabolic disorders. The ratio influences the activity of key enzymes involved in glucose and lipid metabolism, including glycogen synthase, phosphoenolpyruvate carboxykinase (PEPCK), and hormone-sensitive lipase (HSL).

**Why the Correct Answer is Right**
When the Insulin: Glucagon ratio is low, it indicates a state of glucagon dominance. This leads to the activation of enzymes involved in gluconeogenesis and lipolysis, such as PEPCK and HSL, respectively. PEPCK is a key enzyme in the gluconeogenic pathway, catalyzing the conversion of oxaloacetate to phosphoenolpyruvate, thereby promoting glucose production in the liver. On the other hand, HSL is responsible for the breakdown of triglycerides to fatty acids and glycerol, contributing to lipolysis.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not directly relate to the Insulin: Glucagon ratio and its effect on glucose metabolism.
**Option B:** This option is incorrect because it is not directly involved in the regulation of glucose metabolism in response to changes in the Insulin: Glucagon ratio.
**Option C:** This option is incorrect because it is not the correct enzyme associated with the low Insulin: Glucagon ratio.

**Clinical Pearl / High-Yield Fact**
In critical care settings, maintaining an optimal Insulin: Glucagon ratio is crucial for managing glucose homeostasis, particularly in patients with diabetes or those undergoing stress-induced hyperglycemia.

**Correct Answer:** C. Phosphoenolpyruvate carboxykinase (PEPCK)