Vitamins, coenzymes and cofactors • Primarily organic molecules • May have inorganic component or cofactor • Some work with/are part of an enzyme • Promote or catalyze biochemical reactions • Most cannot be made by human body • Water-soluble = all B vitamins, vitamin C • Vitamins A, D, E, K are lipid-soluble • Most of B vitamins used in 2 o metabolism
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Vitamins, coenzymes and cofactors Primarily organic molecules May have inorganic component or cofactor Some work with/are part of an enzyme Promote or.
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Vitamins, coenzymes and cofactors
• Primarily organic molecules
• May have inorganic component or cofactor
• Some work with/are part of an enzyme
• Promote or catalyze biochemical reactions
• Most cannot be made by human body
• Water-soluble = all B vitamins, vitamin C
• Vitamins A, D, E, K are lipid-soluble
• Most of B vitamins used in 2o metabolism
Thiamine (Vitamin B1)
• Catalyzes decarboxylation of -keto acids, a feature of primary metabolism
• e.g. pyruvic acid → acetaldehyde in glycolysis• pyruvic acid → acetyl-CoA (Fig.2.15 p23 Dewick)
• Helps metabolize carbohydrates• Supports nervous system• Deficiency causes beriberi (neurological disorder)• Found in cereals, wheat germ, beans, nuts, eggs, yeast and vegetables
• Involved in redox rxns of C-C bonds• Metabolism of carbs, fat, protein• B2 is widely available in foods, including liver, kidney, dairy products, eggs, yeast,meat, and fresh vegetables• Promotes healthy skin & vision• Deficiency causes eye problems and skin disorders
Niacin/nicotinic acid (Vitamin B3)
• As part of NAD+ system, catalyzes redox rxns of alcohols/carbonyl compounds
• Degradation of L-Trp niacin• (Fig 6.29, p 312 Dewick)• Needed for general metabolism, health of
skin, nervous & digestive system• Found in meats, fish, yeast, eggs, dairy,
– oral lesions, diarrhea, dermatitis, and dementia
Panthothenic acid (Vitamin B5) is part of Coenzyme A
• Synthesis of fatty acids (acetate pathway), some peptides, phenylpropanoids, isoprenoids• Fat, carbs and protein metabolism• Very widely distributed throughout foods,yeast, liver, and cereals provide rich sources.• Deficiency is rare• Vitamins B3, B5, B6 and biotin are thought to promote healthy hair and prevent hair loss
Relationship between one-C metabolism, B-vitamins and health
• One-C metabolism (methylation) is a key reaction in formation of both primary and secondary metabolites in plants & animals, also involved in DNA repair and detoxification pathways
• Elevated homocysteine levels in humans are an indicator (marker) of faulty one-C metabolism
• Homocysteine (HCys) is made from methionine (L-Met), but much of the HCys must be cycled back to L-Met
• Decreased formation of L-Met and SAM result in decreased methylation
• Decrease in the methylation pathway is associated with increased risk of cardiovascular disease, Alzheimer’s disease and some cancers.
• High HCys levels are also thought to be linked to increased production of reactive oxygen species that damage tissues
• Adequate supply of folate (B9), B12 and B6 in diet is necessary to maintain proper HCys metabolism.
H
S
COOH
H2N
Homocysteine
Selhub, J. 2002. The Journal of Nutrition, Health and Aging, 6: 39-41
Biotin (Vitamin H): functions as a carboxyl group carrier
Ex: transforms acetyl-CoA to malonyl-CoA (acetate pathway)
Found in eggs, liver, kidney, yeast, cereals, milkAlso produced by intestinal microfloraDeficiency is rare, but could lead to dermatitis and hair loss