Page 58 - General Biochemistry

Vitamins and coenzymes

• Thiamine (vitamin B1)

Thiamine pyrophosphate (TPP) is the biologically active form of vitamin B1. It acts
as co-enzyme for:

• Transketolase
• Pyruvate dehydrogenase complex
• -ketoglutarate dehydrogenase complex

Thiamine deficiency leads to impairment of oxidative decarboxylation of pyruvate
and α-ketoglutarate, which are important for ATP production in nervous tissues.

This results in impaired nerve cell function leading to beriberi, characterized by
chronic peripheral neuritis.

2. Riboflavin (vitamin B2)

• The two biologically active forms of riboflavin are flavin mononucleotide
(FMN) and flavin adenine dinucleotide (FAD), formed by the transfer of an
adenosine monophosphate moiety from ATP to FMN.

• FMN/FAD act as co-enzymes in oxidation-reduction reactions in which they
undergo reduction to FMNH2/FADH2 by accepting two hydrogen atoms from
2 adjacent carbons creating a double bond.

• Riboflavin deficiency is not associated with a major human disease.
• symptoms include dermatitis, cheilosis (fissuring at the corners of the mouth)

and glossitis (the tongue appears smooth and purplish).

57