Riboflavin

 

Discovery in Milk

• Around 1879–1912, various researchers noted that  milk contained a yellow-green fluorescent pigment.

• In 1920, scientists called this pigment lactoflavin (from lac = milk, flavus = yellow).

• This pigment was isolated from whey (the liquid part of milk after curdling).

🔹 Identification as Riboflavin

• By 1933, German chemists Richard Kuhn and Paul György purified and characterized lactoflavin’s chemical structure.

• They found that it was part of the vitamin B complex and renamed it riboflavin — “ribo” from ribose (a sugar in its structure) and “flavin” from its yellow color.

Riboflavin: Energy

Riboflavin (vitamin B₂) is essential for energy production because it forms the core of two important coenzymes:

1. FMN (Flavin Mononucleotide)

2. FAD (Flavin Adenine Dinucleotide)

These coenzymes are prosthetic groups for many enzymes that drive energy metabolism.

🔹 Role in Energy Production

1. Carbohydrate Metabolism
• Riboflavin-derived FAD acts in the Krebs cycle.
• Example: Succinate dehydrogenase converts succinate → fumarate, reducing FAD → FADH₂.
2. Fat Metabolism
• In β-oxidation of fatty acids, acyl-CoA dehydrogenase uses FAD to start the breakdown, producing FADH₂.
3. Protein Metabolism
• Amino acids feed into the Krebs cycle, with several steps requiring FAD-containing enzymes.
4. Electron Transport Chain (ETC)
• FADH₂ donates electrons directly to complex II (succinate-Q reductase).

Each FADH₂ yields ~1.5 ATP (less than NADH, which yields ~2.5 ATP) because it enters the ETC later

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