Overview Examples B1 (thiamine: TPP) B2 (riboflavin: FAD and FMN) B3 (niacin: NAD+) B5 (pantothenic acid: CoA) B6 (pyridoxine: PLP) B12 (cobalamin) C (ascorbic acid) biotin folate Characteristics when consumed in excess are eliminated in the urine exceptions are B12 and folate (stored in liver) B-complex deficiencies often result in dermatitis, glossitis, diarrhea Vitamin B1 (Thiamine) Edematous legs of a patient with wet beriberi. Function a cofactor for several enzymes such as thiamine pyrophosphate (TPP) pyruvate dehydrogenase (glycolysis) α-ketoglutarate dehydrogenase (TCA cycle) transketolase (HMP shunt) branched-chain AA dehydrogenase (metabolism of Val, Leu, Ile) Deficiency causes alcoholism login to view 2 more bullets malnutrition login to view 1 more bullet symptoms impaired glucose breakdown due to decreased activity of pyruvate dehydrogenase login to view 2 more bullets Wernicke's syndrome login to view 1 more bullet Korsakoff's syndrome login to view 1 more bullet beriberi login to view 7 more bullets diagnosis login to view 4 more bullets management login to view 5 more bullets Vitamin B2 (Riboflavin) Function cofactor for oxidation and reduction (e.g., FADH2) succinate dehydrogenase precursor to FAD and FMN involved with many dehydrogenase enzymes Deficiency causes severe malnourishment symptoms cheilosis (inflammation of the lips and scaling and fissures at the corners of the mouth) corneal vascularization dry skin magenta-colored tongue Vitamin B3 (Niacin) Function constituent of NAD+and NADP+ (used in redox reactions) derived from tryptophan involved with many dehydrogenase enzymes synthesis requires vitamin B2 and B6 Deficiency causes diets low in tryptophan or niacin login to view 1 more bullet Hartnup disease login to view 1 more bullet malignant carcinoid syndrome login to view 1 more bullet INH therapy login to view 1 more bullet symptoms glossitis severe deficiency leads to pellagra (3 D's) login to view 1 more bullet Excess causes nicotinic acid given at high doses as hyperlipidemic treatment (raised HDL) symptoms facial flushing login to view 1 more bullet intrahepatic cholestasis hyperglycemia hyperuricemia Vitamin B5 (Pantothenate) Function component of coenzyme A required for many enzymatic processes fatty acid synthase (fatty acid metabolism) acyl transferases pyruvate dehydrogenase (PDH) α-ketoglutarate dehydrogenase (TCA cycle) Deficiency rare symptoms dermatitis, enteritis, alopecia, and adrenal insufficiency Vitamin B6 (Pyridoxine) Function converted to pyridoxal phosphate, a cofactor used in transamination (e.g., ALT and AST in protein catabolism) decarboxylation reactions glycogen phosphorylase cystathionine synthesis heme synthesis required for the synthesis of niacin from tryptophan Deficiency causes INH (isoniazid) oral contraceptives goat milk chronic alcoholism symptoms convulsions, hyperirritability, peripheral neuropathy, sideroblastic anemias, cheilosis or stomatitis Vitamin B12 (Cobalamin) Function cofactor for homocysteine methyltransferase transfers CH3 groups as methylcobalamin cofactor for homocysteine + N-methyl THF → methionine + THF cofactor for methylmalonyl-CoA mutase metabolism of propionate (odd-chain fatty acid degradation) at the conversion of methylmalonyl CoA → succinyl CoA folate not directly involved in this pathway megaloblastic anemia with an elevated methylmalonyl CoA indicates B12 deficiency as opposed to folate metabolism of Val, Met, ILe, Thr Source found only in animal products several years of reserves stored primarily in the liver Deficiency causes pernicious anemia login to view 2 more bullets gastric bypass surgery login to view 1 more bullet resection of terminal ileum login to view 1 more bullet malabsorption login to view 1 more bullet bacterial overgrowth of terminal ileum diphyllobothrium latum (parasite) login to view 1 more bullet vegan diets use Schilling test to detect etiology of the deficiency login to view 1 more bullet symptoms macrocytic, megaloblastic anemia login to view 1 more bullet hypersegmented PMNs neurologic symptoms due to abnormal myelin login to view 5 more bullets Folic Acid Function converted to tetrahydrofolate (THF), a coenzyme for 1-carbon transfer/methylation reactions important for the synthesis of nitrogenous bases in DNA and RNA (thymidylate synthase) recall: uridine + methyl group = thymidine Deficiency most common vitamin deficiency in the United States absorbed in the jejunum via the action of intestinal conjugase causes dietary deficiency login to view 2 more bullets seen in alcoholism and pregnancy login to view 1 more bullet deficiency can be caused by several drugs login to view 1 more bullet findings macrocytic, megaloblastic anemia hypersegmented neutrophils homocysteinemia login to view 1 more bullet no neurologic symptoms + normal methylmalonic acid level (as opposed to vitamin B12 deficiency) deficiency in pregnancy causes fetal neural tube defects login to view 1 more bullet Biotin Function cofactor for carboxylation enzymes (adds a 1-carbon group) pyruvate carboxylase login to view 2 more bullets acetyl-CoA carboxylase login to view 2 more bullets propionyl-CoA carboxylase login to view 2 more bullets Deficiency relatively rare causes antibiotic use excessive ingestion of raw eggs login to view 1 more bullet symptoms dermatitis, alopecia, enteritis, lactic acidosis Vitamin C (Ascorbic Acid) Function antioxidant regenerates vitamin E ↓ oxidation of LDL keeps iron in Fe2+ reduced state ↑ intestinal absorption collagen synthesis essential for hydroxylation of proline and lysine prolyl and lysyl hydroxylases addition of hydroxyl group allows for hydrogen bonding between fibers without cross-linking triple helix shape cannot form synthesis of norepinephrine necessary for dopamine β-hydroxylase login to view 1 more bullet hepatic synthesis of bile acids keeps THF in reduced form protects against nitrosylation of amides occurs in the stomach with presence of food preservatives nitrosamines/amides are carcinogenic Source found in fruits and vegetables British sailors carried limes to prevent scurvy Deficiency causes diet lacking citrus fruits and green vegetables infants on formula that is boiled too long login to view 1 more bullet cigarette smoking symptoms scurvy login to view 2 more bullets infantile scurvy login to view 2 more bullets Excess symptoms formation of renal calculi made from calcium oxalate (vitamin excreted as oxalate) diarrhea, nausea, vomiting excess iron absorption in those predisposed (hemochromatosis, repeat blood transfusions) S-Adenosylmethionine (SAM) Not a vitamin but an important cofactor Synthesis ATP + methionine → SAM regeneration of methionine (and thus SAM) is dependent on vitamin B12 and folate Function SAM transfers methyl units similar to THF SAM is required for the conversion of NE to epinephrine