Degradation of Riboflavin to Lumiflavin and Lumichrome

 Riboflavin (vitamin B2) can degrade into lumiflavin and lumichrome under certain conditions such as exposure to light, especially ultraviolet (UV) light. Here's how this degradation occurs:

1. Riboflavin Structure

Riboflavin consists of a flavin (isoalloxazine) ring attached to a ribityl side chain. It is sensitive to light, which can cause its breakdown.

2. Degradation to Lumiflavin

• Reaction Conditions: Riboflavin degrades to lumiflavin when exposed to UV light, particularly in an alkaline environment (basic pH).
• Mechanism: UV light induces the cleavage of the ribityl side chain, leading to a structural change where a portion of the molecule is altered but the flavin ring is retained.
• Product: Lumiflavin is formed, a fluorescent yellow compound. It is a photoproduct with the flavin core intact but with the side chain altered or removed.

3. Degradation to Lumichrome

• Reaction Conditions: In acidic or neutral conditions, or under certain enzymatic reactions, riboflavin can degrade to lumichrome when exposed to light.
• Mechanism: The ribityl side chain of riboflavin is cleaved off, leaving behind only the core isoalloxazine (flavin) ring system.
• Product: Lumichrome is the resulting compound, which lacks the ribityl chain and is a more compact derivative of riboflavin.

Summary of the Reactions:

• Riboflavin → Lumiflavin: Exposure to UV light in alkaline conditions.
• Riboflavin → Lumichrome: Exposure to UV light in neutral or acidic conditions.

Both lumiflavin and lumichrome are photodegradation products of riboflavin, but their formation depends on the environmental pH and light exposure.