Major Gluconeogenic Substrate

The major substrate of glucose in gluconeogenesis-

Correct Answer: Propionate

In ruminants, the major substrate for gluconeogenesis (hepatic glucose synthesis) is Propionate — a 3-carbon VFA produced during ruminal fermentation of carbohydrates.

Why Propionate is Critical for Ruminants?

• Ruminants absorb very little dietary glucose (most carbohydrate is fermented to VFAs in rumen)
• The liver must synthesize nearly ALL of the animal's glucose requirement via gluconeogenesis
• Propionate (3C) → Propionyl-CoA → Succinyl-CoA (requires Vitamin B₁₂) → enters Krebs cycle → Oxaloacetate → Glucose
• Vitamin B₁₂ deficiency → impaired propionate utilization → glucose deficiency → ketosis

Gluconeogenic Substrates by Importance (Ruminants)

• Propionate > Lactate > Glucogenic amino acids > Glycerol

Important Precursors Summary

• Glucose (ruminants): Propionate
• Cholesterol: Acetyl-CoA
• Steroid hormones + Vitamin D: Cholesterol
• Prostaglandins: Arachidonic acid
• Thyroxin + Catecholamines: Tyrosine
• Niacin: Tryptophan
• Vitamin C: Hexose sugar