BIOCHEMISTRY—NUTRITION

BIOCHEMISTRY—NUTRITION (continued)
Vitamin B2 (riboflavin) Deficiency Angular stomatitis (inflammation of oral mucous The 2 C’s. linings), Cheilosis (inflammation of lips), FAD and FMN are derived from Corneal vascularization. riboFlavin (B2 =2 ATP). Function Cofactor in oxidation and reduction (e.g., FADH2).
Vitamin B3 (niacin) Deficiency Niacin is made by the body from tryptophan. Pellagra’s symptoms are the 3 Synthesis requires B6. Pellagra can be caused by D’s: Diarrhea, Dermatitis, Hartnup disease (↓tryptophan absorption), Dementia (also beefy malignant carcinoid syndrome (↑tryptophan glossitis). metabolism), and INH (↓vitamin B6). NAD derived from Niacin Function Constituent of NAD+, NADP+ (used in redox (B3 =3 ATP). reactions). Derived from tryptophan using vitamin B6.
Vitamin B5 (pantothenate) Deficiency Dermatitis, enteritis, alopecia, adrenal insufficiency. Function Constituent of CoA (a cofactor for acyl transfers) Pantothen-A is in Co-A. and component of fatty acid synthase.
Vitamin B6 (pyridoxine) Deficiency Convulsions, hyperirritability (deficiency inducible by INH and oral contraceptives), peripheral neuropathy. Function Converted to pyridoxal phosphate, a cofactor used in transamination (e.g., ALT and AST), decarboxylation reactions, glycogen phosphorylase, and heme synthesis. Required for the synthesis of niacin from tryptophan.
Vitamin B12 (cobalamin) Deficiency Macrocytic, megaloblastic anemia; neurologic Found only in animal products. symptoms (optic neuropathy, subacute combined Vitamin B12 deficiency is  degeneration, paresthesia); glossitis. usually caused by Function Cofactor for homocysteine methyltransferase  malabsorption (sprue, (transfers CH3 groups as methylcobalamin) enteritis, Diphyllobothrium and methylmalonyl-CoA mutase. latum), lack of intrinsic factor Stored primarily in the liver. (pernicious anemia, gastric Very large reserve pool (several years). bypass surgery), or Synthesized only by microorganisms. absence of  terminal ileum (Crohn’s disease). Use Schilling test to detect the etiology of the deficiency. Abnormal myelin is seen in B12 deficiency, possibly due to ↓methionine or ↑ methylmalonic acid (from metabolism of accumulated methylmalonyl-CoA).
BIOCHEMISTRYHIGH-YIELD PRINCIPLES
Homocysteine + N-methyl THF
B12
Methionine + THF
Methylmalonyl-CoA
B12
Succinyl-CoA
79
Folic acid Deficiency Most common vitamin deficiency in the United FOLate from FOLiage. States. Eat green leaves (because folic Macrocytic, megaloblastic anemia (often no acid is not stored very long). neurologic symptoms, as opposed to vitamin Supplemental folic acid in B12 deficiency). early pregnancy reduces Function Coenzyme (THF) for 1-carbon transfer; involved neural tube defects. in methylation reactions. Important for the synthesis of nitrogenous bases in DNA and RNA.
Biotin Deficiency Dermatitis, enteritis. Caused by antibiotic use, “AVIDin in egg whites excessive ingestion of raw eggs. AVIDly binds biotin.” Function Cofactor for carboxylations: 1. Pyruvate →oxaloacetate 2. Acetyl-CoA →malonyl-CoA 3. Propionyl-CoA →methylmalonyl-CoA
Vitamin C (ascorbic acid) Deficiency Scurvy––swollen gums, bruising, anemia, poor British sailors carried limes to wound healing. prevent scurvy (origin of the Function Necessary for hydroxylation of proline and lysine in word “limey”). collagen synthesis. Facilitates iron absorption by keeping iron in Fe2+ reduced state (more absorbable). Necessary as a cofactor for dopamine β-hydroxylase, which converts dopamine to NE.
Vitamin D D2 =ergocalciferol, consumed in milk. Remember that drinking milk D3 =cholecalciferol, formed in sun-exposed skin. (fortified with vitamin D) is 25-OH D3 =storage form. good for bones. 1,25 (OH)2 D3 (calcitriol) =active form. Deficiency Rickets in children (bending bones), osteomalacia in adults (soft bones), and hypocalcemic tetany. Function ↑intestinal absorption of calcium and phosphate. Excess Hypercalcemia, loss of appetite, stupor. Seen in sarcoidosis, a disease where the epithelioid macrophages convert vitamin D into its active form.
Vitamin E Deficiency ↑fragility of erythrocytes, neurodysfunction. Vitamin E is for Erythrocytes. Function Antioxidant (protects erythrocytes from hemolysis).
HIGH-YIELD PRINCIPLES BIOCHEMISTRY
80
BIOCHEMISTRY—NUTRITION (continued)
Vitamin K Deficiency Neonatal hemorrhage with ↑PT and ↑aPTT but K for Koagulation. Note that normal bleeding time, because neonates have the vitamin K–dependent sterile intestines and are unable to synthesize clotting factors are II, VII, vitamin K. IX, X, and protein C and S. Function Catalyzes γ-carboxylation of glutamic acid residues Warfarin is a vitamin K on various proteins concerned with blood clotting. antagonist. Synthesized by intestinal flora. Therefore, vitamin Neonates are given vitamin K deficiency can occur after the prolonged use of K injection at birth to prevent broad-spectrum antibiotics. hemorrhage.
Zinc deficiency Delayed wound healing, hypogonadism, ↓adult hair (axillary, facial, pubic); may predispose to alcoholic cirrhosis.
Ethanol metabolism Fomepizole inhibits alcohol dehydrogenase. Disulfiram (Antabuse) inhibits acetaldehyde dehydrogenase (acetaldehyde accumulates, contributing to hangover symptoms). NAD+ is the limiting reagent. Alcohol dehydrogenase operates via zero-order ` kinetics.
Ethanol Ethanol metabolism ↑NADH/NAD+ ratio in liver, causing diversion of pyruvate hypoglycemia to lactate and OAA to malate, thereby inhibiting gluconeogenesis and leading to hypoglycemia. This altered NADH/NAD+ ratio is responsible for the hepatic fatty change (hepatocellular steatosis) seen in chronic alcoholics (shunting away from glycolysis and toward fatty acid synthesis, which normalizes the ratio).
Kwashiorkor vs. Kwashiorkor––protein malnutrition resulting in skin Kwashiorkor results from a marasmus lesions, edema, liver malfunction (fatty change). protein-deficient MEAL: Clinical picture is small child with swollen belly. Malnutrition Marasmus––energy malnutrition resulting in Edema tissue and muscle wasting, loss of subcutaneous Anemia fat, and variable edema. Liver (fatt