BC Exam 3

What is a micronutrient?

What is a micronutrient?

Nutrients essential to health needed in small amounts

What is a Vitamin?

• Essential for optimal health (vita = life)- Get from diet or gut microbes- Most are protein cofactors

What are the types of protein cofactors?

• Mobile = substrate- Bound = stable; can be covalent or non covalent- Free = act independently of proteins

Why was the discovery of thiamin so important to the vitamin hypothesis?

-- Learned that a single compound can cure disease- Thiamin is the first isolated vitamin (cured beri beri)

What is meant by a "conditional" vitamin and which vitamins fall into that category?

-- Vitamins that can be made when needed- Niacin - can make from tryptophan (conversion is low)- Vitamin D - UV

What is a vitamer?

Slight form variation in vitamin (ex. 3 forms of B6)

What are the 4 basic functions of vitamins?

-- Carrier- Catalyst- Sensor (metabolic/ environment conditions)- Signal (developmental or physiological state)

What distinguished a carrier from a catalyst?

• Carrier = bind and release things unchanges- Catalyst = bind and change substrates

In evolutionary terms, why did vitamins become essential to health?

• We have a gene to make vitamins but it no longer is expressed- When we lost the expression of the gene, there were no consequences because we got enough in the diet

Where do you find B6 (pantothenate) in the body?

• Component of coenzyme A (carrier of acetyl or Acyl groups as high energy ester bonds → carries and hands them off)- Anything with CoA is a B5 dependent reaction- Also used in fatty acid synthase as phosphopantetheine

What is the structure of CoA?

Reactive SH group, pantothenate unit (dietary part), ADP + P

What synthesizes pantothenate?

Bacteria and plants

What parts of the TCA cycle involve B5?

• Pyruvate dehydrogenase (adding a CoA) - oxidative decarboxylation- alpha-ketoglutarate dehydrogenase (add CoA)- Alpha-ketobutyrate dehydrogenase → degradation of threonine into alpha-ketoglutarate and then add adds CoA to make propionyl CoA

How is B5 involved in fatty acid beta-oxidation?

Adding CoA to FAs during carnitine transfer

How is B5 involved in fatty acid synthesis?

• Acetyl CoA used as building block- FAS has two pantothenate containing sites on condensing enzymes- Uses phosphopantetheine and NOT CoA

Is B5 bound, mobile or free?

-- Depends- Bound when used as acyl carrier protein for FAs- CoA is a carrier- mobile

What is the function of B5?

Carrier

What doe B5 act on?

Acyl and acetyl groups

What is the reactive site of B5's cofactor molecules?

-- High energy thioester- Binds to acyl and acetyl groups for transfer

What is B5 deficiency?

• Rare- abundant is most plant and animal foods- Seen with severe malnourishment (alcoholism, malabsorption diseases)- Burning feet syndrome → neurodegenerative

What form is pantothenate in the diet? How does it circulate? How do tissues use it

• Diet = pantothenate, phosphopantetheine, and CoA- Absorbed and circulates as pantothenate (phosphopantetheine and CoA hydrolyzed; active transport)- Converted to CoA in tissues

Does intravenous micronutrient therapy work?

No, had same effect as placebo

How do we know what is "optimal" level of micronutrients for individuals (5 strategies to assess a person's nutrient status)?

• Direct measure of nutrient (blood, hair, fingernails)- Direct assessment of its homeostasis (urine excretion, partitioning of bolus)- Direct measure of biochem actions (enzymatic reactions, gene expression levels)- Indirect measure of physiological action (excretion of pathway metabolites, blood clotting)- Epidemiological relationships (diet recalls, intake vs. disease)

What are the limitations of the current approach of defining dietary reqiurements

Even with RDA and UL, still 2.5% of population not getting adequate amounts

What is the assessment for pantothenate?

Direct measurement of nutrient- Blood levels

What are the most fundamental products of energy metabolism?

Electrons

Where do we find riboflavin in the body? What is it used for?

• Enzyme cofactor (flavoproteins) — tightly bound to enzymes- Redox reactions — dehydrogenases- Energy generation- TCA, ETC, FA oxidation

What is the difference between FMN and FAD structure?

FAD molecule contains two nucleotide components, whereas FMN contains only one nucleotide component

What are some examples of riboflavin-dependent reactions? What is it used for?

• ETC— first step requires FMN- Succinate dehydrogenase (TCA)— FADH2 is part of Complex II (AKA succinate dehydrogenase)- Acyl Coa Dehydrogenase in FA ox. (parth of the enzyme)- Pyruvate dehydrogenase (gives electrons)- Alpha-ketoglutarate dehydrogenase (NAD+ picks up protons from FADH2)

Is riboflavin bound, mobile, or free?

Bound to enzymes

Is riboflavin a carrier, catalyst, sensor, or signalor?

Carrier

What is the constituent of riboflavin?

Electrons

What is it about the structure of riboflavin that allows it to carry out its function?

• Double sided N- Double bonds allow electron donation

How common is riboflavin deficiency? What causes it?

• Uncommon because synthesized by plants and microbes, mostly seen in newborns (neonates with jaundice and given blue light phototherapy which destroys riboflavin)- Light destroys riboflavin (why milk is in opaque containers)

What are the forms of riboflavin in the diet? How is it absorbed? What form circulates in cells and what form is used in tissues?

• Diet: riboflavin (plants), FMN and FAD (animals)- Converted to riboflavin in intestine- Active transport- Circulate as riboflavin- Converted to FMN and then FAD in tissues

How do we measure optimal riboflavin?

• Direct measure of biochem actions → Glutathione reductase reaction- Test activity with and without added FAD- If added FAD increases activity more than 40% it indicates deficiency

Is niacin bound, mobile, or free?

Mobile

Is niacin a carrier, catalyst, sensor, or signalor?

Carrier

What is the constituent of niacin?

electrons

Where do we find niacin in the body? What is it used for?

• Enzyme cofactor (substrate = mobile)- Component in NAD+, NADH, NADP+, NADPH- Involved in redox reactions- Generally dehydrogenases- Substrate for sirtuin proteins

Why have both NAD+ and NADP+ forms?

• Division of labor- NAD+: levels highest in mitochondria, mostly found as NAD+ (oxidized form), involved in catabolic reactions- NADP+: levels highest in cytosol, mostly found as NADPH (reduced form), involved in antioxidant and biosynthetic reactions, source of electrons for redox reactions

How does niacin carry electrons?

• N gives carbon at top of niacin ring resonance stabilization

What are some examples of niacin-dependent reactions? What is it used for?

• Pyruvate dehydrogenase: pick up electrons from FAD+- Alpha-ketoglutarate dehydrogenase (TCA): pick up electrons from FAD+- Degradation of threonine (also alpha-ketoglutarate dehydrogenase): pick up electrons from FAD+- Beta-hydroxyacyl CoA dehydrogenase: pick up electrons from FAD+- ETC: handing off electrons to FMN

What are the vitamers of niacin and which is the biochemically active form?

• Nicotinic acid- Nicotinamide (active form)

How do the roles of niacin in energy metabolism differ from those of riboflavin?

• Both transport electrons- Riboflavin is within enzymes- Niacin shuttles

How can we get niacin?

• Diet and synthesis

How is niacin found in diet? How is it absorbed? How is it transported in blood? What is it converted to?

• Found in foods as nicotinic acid or nicotinamide- Active transport- Transported in blood as nicotinamide- Converted in all cells as NAD+ and NADP+

How can niacin be synthesized?

• Synthesized in liver- Made from tryptophan (conditional vitamin)- 90g protein → 1% tryptophan (90mg) → 15mg niacin (1mg niacin per 60mg tryptophan)- This is why the RDA is calculated in terms of niacin equivalents (Also includes tryptophan)

What is niacin deficiency?

• Pellagra- Symptoms: 4 D's → dermatitis, diarrhea, dementia, and death- Contributing factors: niacytin (niacin bound to carbs, ex. corn), poor protein source diet, medications, malabsorptive disorders, genetics

How is niacin assessed?

Direct assessment of its homeostasis →Urinary excretion of metabolites

What are the pharmacologic benefits of niacin?

• 2g/day nicotinic acid (100x RDA) can lower serum cholesterol, lower TGs, increase HDL (nicotinamide not effective)- This is due to sirtuins- enzymes that catalyze deacetylation (HDACs) and ADP-ribosylation reactions- Regulators of cellular energy and redox status- Post-translational modification to proteins- Important for tumor suppressor genes

How to sirtuins work?

• Deacetylase reaction: protein-acetyl + NAD+ → protein (no acetyl group) + 2-O-acetyl ADP ribose + Niacin- ADP ribosylation reaction: protein + NAD+ → protein-ADP ribose + Niacin- sirtuins- enzymes that catalyze deacetylation (HDACs) and ADP-ribosylation reactions- Regulators of cellular energy and redox status- Post-translational modification to proteins- Important for tumor suppressor genes

How many calories in 1 g of alcohol?

• 7 kcal per gram- Average US consumption ~5% kcal intake

What are the "active" ingredients in alcohol?

• Ethanol- Byproducts: Acetaldehyde and acetate

Where is alcohol absorbed?

• Absorbed in stomach and small intestine- Absorbed efficiently and quickly

Where is alcohol metabolized?

• Some metabolized in stomach and intestinal cells (~20%) → alcohol/aldehyde dehydrogenase- The rest is metabolized in the liver → alcohol/aldehyde dehydrogenase and microsomal ethanol oxidizing system- 2 systems of alcohol metabolism → both are niacin dependent

How does the alcohol/aldehyde dehydrogenase system work?

• Two enzymes: alcohol dehydrogenase and aldehyde dehydrogenase- NAD and zinc dependent- Generates high NADH and acetyl CoA- Occurs in stomach, small intestine, and liver under moderate alcohol consumption- Women, older people, and some ethnic groups have low ADH and asians often have low ALDH which means it is less able to clear alcohol per hour

How does the microsomal ethanol oxidizing system work?

• Metabolism when alcohol consumption is heavy and chronic when system I is overwhelmed (alcohol/aldehyde dehydrogenase system) → mechanism of alcohol tolerance- Occurs only in liver (enzymes in the ER)- Iron and NADPH dependent- Still requires ALDH- Generates acetaldehyde, acetyl CoA and NADH (and regenerates FAD)- Sloppy → generates reactive oxygen

How does alcohol lead to ketone synthesis?

• Systems I and II generate high acetyl CoA but alcohol metabolisms slows the TCA cycle- Ketones produced through overflow pathway- Exhale ketones in breath → smell alcohol on breath

What are the health effects of alcohol?

• Heavy drinking is >2 drinks- Impairs brain function: increases accidents, decreases judgement, decreases productivity- Hangovers- Liver disease: fatty liver and cirrhosis- Contributes to malnutrition- Increases cancer, CVD, stroke, depression, anxiety risk, fetal alcohol syndrome- Problem with even moderate consumption

What is fatty liver disease?

• early stage damage in alcoholism- fat deposits in liver- Symptoms- fatigue, nausea- Reversible

How does alcoholism cause fatty liver?

• Poor food choices- High caloric content of alcohol- Systems I and II increase NADH:NAD ratio → this slows beta oxidation, the TCA cycle, and increases GTP (TG precursor)- Systems I and II increase citrate levels: acetate → acetyl CoA → citrate which activates Acetyl CoA carboxylase allostery (FA syn)

Why does high NADH:NAD slow beta-oxidation?

• Beta Hydroxyacyl CoA dehydrogenase- Product inhibition (NADH)

Why does high NADH:NAD slow TCA?

• NAD dependent reactions- ex. alpha-ketoglutarate dehydrogenase

Why does alcohol increase FA synthesis?

• Citrate builds up- Sends acetyl CoA to fat synthesis

Why does NADH:NAD ration increase GTP?

• Glycerophosphate dehydrogenase- High NADH pushes the reaction to make more GTP- Substrate stimulation

What is liver cirrhosis?

• Structural damage to liver cells- Increased scar tissue in liver leading to loss of function- Irreversible

Why does alcohol consumption cause cirrhosis?

• Acetaldehyde is more toxic than alcohol- Covalently binds to proteins and DNA and interferes with their function- major source of tissue damage- MEOS produces reactive oxygen → oxidant damage proteins, lipids, and DNA

Why can alcoholism cause malnutrition?

-- Dietary: empty calories that displace food, poor food choices, lower food purchasing resources- Toxicity to liver: inflammation of enterocytes leading to pancreatitis, interferes with digestion and absorption- Toxicity to stomach and small intestines: impairs vitamin synthesis and activation (niacin and thiamin; increases degradation of vitamins (Vitamin A and niacin)

What cancers can alcohol increase your risk of? How does this happen?

• Increases risk of GI cancers, prostrate, and breast cancer- Causes:- Cell irritant → increased mitosis = increased mutation risk- Acetaldehyde is mutagenic → attacks DNA (less active ALDH isozymes linked to cancer risk)

What is fetal alcohol syndrome?

• Number one cause of intellectual disability- Symptoms: smaller head circumference, altered facial features, abnormal joints and limbs, poor coordination, problems with learning, short memories- Mechanism: fetus cannot metabolize alcohol and it kills neurons and other cells during sensitive periods of development

What are the roles of niacin in alcohol metabolism?

NAD is needed for systems I and system II

Why does heavy alcohol disrupt metabolism?

Damages the liver cells

How did ethanol metabolism evolve?

• Most promotes cannot do this- Gene developed in early primates when climate changes forced greater terrestrialism

Is Thiamin bound, mobile, or free?

Bound- enzymatic cofactor

Is Thiamin a carrier, catalyst, sensor, or signalor?

Catalyst

What is the constituent of thiamin?

Alpha-keto acids

What is the reactive site of thiamin?

• N=C-S- C is a reactive carbon- grabs other carbons

What is the structure of thiamin?

• N=C-S- Diphosphate addition needed to activate enzyme (occurs in liver)

What are the major reactions using thiamin?

• Pyruvate dehydrogenase- Alpha ketoglutarate dehydrogenase- Alpha ketobutyrate dehydrogenase- BCAA alpha-keto acid dehydrogenase- All examples of oxidative decarboxylation (CO2 removed)

What are the specific roles of the vitamins used by pyruvate dehydrogenase?

• Thiamin (TAD)- removes CO2- Niacin- NAD+ → NADH- Riboflavin- FAD- Pantothenate- gives CoA- Note: not net change in TPD of FAD (dehydrogenase complex) so not mentioned in reaction

Why would thiamin deficiency be more disruptive to metabolism even though it has fewer roles?

More disruptive because it is harder to sense the deficiency

What are the parts of the pyruvate dehydrogenase complex?

E1 (Thiamin), E2 (CoA, Lipoamide), E3 (FAD and NAD)

What is maple syrup urine disease?

• Defect in BCAA metabolism (Thiamin dependent) causing bottle neck of reaction and BCAA to leak into urine (sweet smell)- Common in amish

What are the diseases caused by thiamin deficiency?

• Beri Beri → weakness, thermoregulation problems, CV failure- Wernicke's Encephalopathy → Dementia, memory problems, nerupathy; common in alcoholics- Infant botulism → sees better results with thiamin supplementation (botulism toxin blocks acetylcholine release, thiamin deficiency blocks acetylcholine synthesis)

What are the factors that can cause thiamin deficiency?

• Alcohol (dietary and toxicity mechanisms) → interfere with absorption and thiamin is activated in the liver- Tannins → bind to thiamin and lower absorption- Thiaminases → enzymes that destroy thiamin (raw fish and shellfish, cabbage, broccoli, nardoo fern)

How is thiamin assessed?

• Widely distributed in food so deficiency is rare- Requirement is affected by energy needs- Direct assessment - Thiamin excretion in urine- Direct measure of biochem actions - Transketolase activity in RBS

What is the main function of Biotin?

• Enzyme cofactor, covalently attached- Required by only 4 enzymes- Adds CO2 to substrates - carboxylases- Uses bicarbonate as its substrate- ATP dependent

What is the reactive and attachment site of biotin?

• Reactive: NH- Attachment: COOH

What are the biotin dependent reactions?

• Pyruvate carboxylase (Pryruvate → OAA)- Propionyl CoA carboxylase (odd chain FAs beta Oxidation and AA degradation to Succinylcholine CoA)- Beta-methylcrotonyl CoA carboxylase (Leucine to beta-methylglutaconyl CoA to Acetoacetae and Acetyl CoA)- Acetyl CoA carboxylase (Acetyl CoA to malonyl CoA)

What is allostery?

• Regulation of an enzyme's activity by metabolites that are neither products nor substrates of the reaction- Communication between metabolic pathways- Major mechanism in regulating metabolism

How is pyruvate carboxylase allosteric?

Activated by acetyl CoA to limit enzyme activity

What is the biotin carrier (BCCP) domain?

• Biotin carboxylation domain: BCCP-biotin + HCO3 + ATP → BCCP-biotin-CO2 + ADP + P- Carboxyltransferase Domain: BCCP-biotin-CO2 + Pyruvate → BCCP-biotin + OAA- Pyruvate carboxylase- Connected by CoA binding site

How does allostery affect biotin?

CoA can bind to CoA binding site on BCCP and cause the two domains to fold to slow the reaction of turning pyruvate to OAA (pyruvate carboxylase)

What foods have biotin?

• Widely found in foods- Liver, eg yolk, green vegetables, and whole grains

What is seen with biotin deficiency?

• Rare- Lethargy, seizures, ataxia, nausea, hair loss, dermatitis

What are the dietary forms of biotin? What form is absorbed?

Blank

Why do raw eggs induce biotin deficiency?

• Contains avidin which is a protein that binds to biotin and blocks its absorption- Used in antibody testing

What enzyme activates biotin?

• Holocarboxylase synthase- Attaches biotin to the enzyme active site (activates it)- Attaches to specific lysine

What enzyme is needed to recycle biotin?

• Biotinidase- Releases biotin from enzyme active site when enzyme is degraded- Needed for absorption in the intestine