• Activated by double phosphporylation to form thiamin pyrophosphate (TPP)
• Function: carbohydrate metabolism
• (1) decarboxylation of a-keto acids (a -ketoglutarate or pyruvate dehydrogenase complex)
• (2) transketolase in pentose pathway – erythrocyte transketolase activity is clinical measure of thiamin activity
• Source: high levels in seeds and grains, although widely distributed in diet
• Deficiency: called beriberi – most often occurs with disease, chemotherapy, or alcoholism
• Can be "wet" or "dry" depending on whether edema is present – other symptoms:
• neurological – weakness, decreased muscle strength (wrist or foot drop), ataxic gait, numbness/tingling in extremities
• called Wernicke-Korsokoff encephalopathy
• cardiovascular – cardiac palpitations, chest pain, dyspnea on exertion, edema, danger of acute circulatory failure
• gastrointestinal – anorexia, nausea, vomiting

• B₂ Þ FAD and FMN, niacin Þ NAD⁺
• FAD and FMN used for a -ketoacid, succinic, or NADH dehydrogenases, amino acid oxidase, fatty acid synthesis/oxidation
• B₂ (flavins) are similar to niacin, but are more versatile:
• they are stronger oxidizing agents, can handle 1 or 2 e^-, and can react directly with oxygen (hydroxylation reactions)
• B₂ is used to keep erythrocyte glutathione reduced, so erythrocyte glutathione reductase activity is a clinical measure of B₂
• B₂ Source: best source is milk – milk is not stored in transparent containers because riboflavin is light sensitive
• also present in collard greens/kale, lean meats, eggs, cheese, liver, yeast
• B₂ Deficiency: usually follows diseases, eating problems, etc. – many symptoms, relationship to metabolism unclear:
• failure to thrive, sore throat, magenta tongue (glossitis), angular stomatosis (lip cracking/fissures at sides of mouth), dermatitis in nose and scrotum, anemia
• Niacin Source: meat, fish, cereals, and pulses
• Niacin Deficiency: pellagra – causes dermatitis, diarrhea, dementia, death

• B₆ (pyroxidine) – transamination reactions
• from cereals, liver, meat, fruits, leafy vegetables
• deficiency: dermatitis, seizures, hyperchomatic/microcytic anemia
• B₁₂ (cobalamin) – formyl group reduction (DNA synth.)
• from milk, meat, liver (requires intrinsic factor)
• deficiency: pernicious anemia, megaloblastic anemia
• Folic acid – involved in DNA (thymidine) synthesis
• from liver and green vegetables
• deficiency: anemia, neural tube defects (pregnancy)
• Pantothenic Acid (Coenzyme A) – carry alkyl groups
• very many sources
• deficiency: dermatitis
• Biotin – carboxylation reactions
• from liver, kidney, yeast extracts
• deficiency: dermatitis

Metabolic Role of B Vitamins