Food Sources, Functions, Key Enzymes, DRIs, & Common Interactions

Micronutrient Biochemistry Exam 2

Riboflavin Food Sources

• Found in milk & meat products, eggs, and enriched grain products

• Mostly available in foods as coenzyme forms FAD & FMN

• Availability in Foods:

  • Meats (especially LIVER)

  • Green vegetables

  • Enriched flour & cereals

• Riboflavin is present in milk & eggs

• Riboflavin in milk & eggs is unstable w/ light exposure & alkaline environments (i.e., baking soda)

• Absorption, Digestion, Transport, & Storage

  • Riboflavin as FAD, FMN, & riboflavin phosphate is freed prior to absorption

  • Absorbed by energy-dependent transporter to proximal small intestine

Riboflavin Functions

1. Flavoproteins in electron transport chain

2. Vitamin B6 metabolism & choline catabolism

3. Used by L-amino oxidase

4. Oxidative carboxylation of pyruvate

5. Succinate dehydrogenase

6. Fatty Acid B-oxidation

7. Sphingosine oxidase, in sphingosine synthesis, requires FAD

8. Coenzyme for an oxidase such as Xanthine Oxidase

9. Synthesis of folate as 5-Methyl Folate

10. Synthesis of Niacin from Tryptophan

11. Glutathione, Thioredoxin, & Ribonucleotide Reductases

12. Some neurotransmitters

Riboflavin (Vitamin B2) Overview

-Precursor of FMN & FAD

-Coenzymes for many reactions

Vitamin K Functions

Vitamin K & Blood Clotting

• Fibrinogen must be converted to fibrin

• The role of vitamin K in the carboxylation of glutamic acid residues

• Anticoagulant (e.g., Warfarin)

  • Diet restricts vitamin K because anticoagulants like Warfarin block vitamin and consuming vitamin K in the diet can counteract the medication’s effectiveness

• Used for Carboxylation Reactions

  • Activates proteins that bring calcium into bone and support calcification

Vitamin K DRIs

• MEN = 120 ug/day

• WOMEN = 90 ug/day

  • These amounts may be inadequate for bone health

• Deficiency:

  • Newborns

  • Malabsorption (Celiac Disease, Crohn’s Disease, Ulcerative Colitis)

  • Antibiotics

• Vitamin K toxicity only occurs w/ synthetic menadione

Folate Interactions

• Interactions w/ other nutrients

  • Synergistic w/ vitamin B12

  • Association w/ disease

  • Methotrexate (antineoplastic drug) is an antagonist of folate

• Metabolism & Excretion

  • Excreted in urine & feces

Folate Functions

• Amino Acid & Choline Metabolism

  • Serine to Glycine degradation

  • Choline degradation

  • Histidine degradation

  • Methionine & SAM synthesis

• Gene Expression

• Purine & Pyrimidine Synthesis/Nucleotide Metabolism

• Associations w/ disease

Dietary Folate Equivalents (DFEs)

1 DFE is equal to:

• 1 ug of food folate

• 0.6 ug of folic acid from supplement or fortified food consumed w/ meal

• 0.5 ug of folic acid from a supplement taken w/o food (on empty stomach)

• State Alternatively, 1 DFE = ug food folate + (1.7*ug folic acid)

Folate RDA

MEN = 400 ug/day

PREGNANCY = 600 ug/day

LACTATING = 500 ug/day

UL = 1 mg synthetic (nonnatural)

Folate Food Sources

• Found in vegetables

  • Higher concentration in raw foods than cooked

• Enriched Foods

  • Fortification began in 1998

  • Now more Americans meeting recommendations

• Bioavailability from foods varies

Iron RDA & Deficiency

• MEN = 8 mg

• WOMEN:

  • PREMENOPAUSAL = 18 mg

  • POSTMENOPAUSAL = 8 mg

  • PREGNANCY = 27 mg

  • LACTATING = 9 mg

• Intake is frequently inadequate w/ these populations:

  • Infants/Young Children

  • Adolescents

  • Menstruating Females

  • Pregnant Women

• Deficiency of iron progresses to iron-deficiency anemia

  • Treatment requires supplementation

Iron Functions

• Hemoglobin & Myoglobin

  • O2 delivery

• Cytochromes & Other Enzymes

  • Involved in electron transport

• Monooxygenases & Dioxygenases

  • Amino Acid Metabolism

  • Carnitine Synthesis

  • Pro-Collagen Synthesis

• Peroxidases

  • Antioxidant Roles

  • Thyroid Hormone Synthesis

• Oxidoreductases

  • Iron is cofactor that facilitates electron transfer in redox reactions

• Other Iron-Containing Enzymes

• Iron as a pro-oxidant

Dietary Sources of Sodium

• Consumed mainly as sodium chloride, w/ small amounts of bicarbonate, citrate, & glutamate

• Sodium Sources:

  • Natural Foods = 10%

  • Table Salt Added = 15%

  • Manufacturing & Processing = 75%

• High Na+: cured meats, soy sauce, canned soups, & processed foods

• Low Na+: fresh fruits & vegetables (vegetarians consume 0.8 g/day)

• Na+ consumption varies among countries:

  • US = 4-18 g/day NaCl

  • JAPAN = 10-20 g/day NaCl

Sodium Functions

1. Maintenance of osmotic pressure

2. Nerve transmission/Impulse conduction

3. Muscle contraction

   -Dietary sodium intake increases urinary excretion of calcium

Sodium Excretion & DRIs

• Excreted by kidneys & sweat

  • Aldosterone controls excretion

• Deficiencies are RARE

  • May occur excessive sweating

• AI: 1500 mg/day

• Tolerable Upper Intake Level: 2300 mg/day

• Measured routinely in labs

  • 24-hour urinary sodium excretion level

Chloride Overview

• Most abundant anion in ECF

• Primary source is sodium chloride

• Almost completely absorbed in intestines

Chloride Functions

1. Formation of HCl

2. Released by WBCs to help destroy foreign substances

3. Exchange anion for HCO3- in RBCs

   -Known as chloride shift

Chloride Intake

• Excreted thru GI tract, skin, & kidneys

  • Losses reflect those of Na+

• AI: 2300 mg/day

• Deficiencies are RARE

• Evaluated thru serum concentrations

  • Dependent on plasma volume

Potassium Adequate Intakes

INFANTS:

• Up to 6 months = 0.4 g/day

• 7 to 12 months = 0.7 g/day

CHILDREN:

• 1 to 3 years = 3.0 g/day

• 4 to 8 years = 3.8 g/day

• 9 to 13 years = 4.5 g/day

• 14 to 18 years = 4.7 g/day

ADULTS:

• 19 to 50 years = 4.7 g/day

• 51 to 70 years = 4.7 g/day

• >70 years = 4.7 g/day

• Pregnancy = 4.7 g/day

• Lactating = 5.1 g/day

Potassium Adequate Intake

• Excretes mainly via kidneys

  • Small amounts in sweat & feces

• Adequate Intake: 4700 mg/day

• Deficiencies result from profound loss of fluids & electrolytes

  • Hypokalemia

• Assessed by plasma/serum potassium concentrations

Dietary Sources of Potassium

VEGETABLES

Sweet Potato

Beans & Lentils

Spinach

FRUITS

Raisins

Plums

Plantains, Bananas

Orange Juice

Potassium Functions

1. Maintenance of negative resting membrane potential

2. Critical for nerve impulses and muscle excitation

3. Cofactor in certain enzymatic reactions (pyruvate kinase)

4. Water & Acid-Base Balance

5. Decreases urinary excretion of calcium