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Nutrition 3330 > 4 B6 and B12 > Flashcards

4 B6 and B12 Flashcards

1
Q

6 related compounds of B6

A

pyridoxal, pyridoxine, pyridoxamine

- and their phosphates

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2
Q

B6 phosphorylated in..

A

foods

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3
Q

B6’s phosphate removed by

A

intestinal enzymes

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4
Q

B6 absorption

A

well absorbed passively

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5
Q

Process that occurs when B6 is absorbed by tissues

A

re-phosphorylated in tissue

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6
Q

Urinary excretion metabolite of B6

A

4-pyridoxic acid

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7
Q

B6 coezyme form

A

pyridoxal phosphate (PLP)

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8
Q

Vitamin needed to convert pyridoxine (related B6 compound) to pyridoxal phosphate (PLP)

A

riboflavin

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9
Q

PLP

A

pyridoxal phosphate

  • coenzyme of B6
  • over 100 PLP dependent enzymes
  • amino acid metabolism
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10
Q

Primary role of B6

A
  • amino acid metabolism
  • Intermediary metabolism (GNG)
  • Tryptophan metabolism
  • synthesis of niacin (ribo also needed - kyneurine pathway)
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11
Q

Schiff Base

A

PLP binds to “lysine” on enzymes via schiff base

  • link formed between PLP aldehyde and enzyme amino group (lysine)
  • forms IMINE group
    R-C=N-R’
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12
Q

B6 roles in metabolism

A

amino acid metabolism

nervous system
- synthesis of neurotransmitters

hormone function
- inhibits by binding to receptors

glycogen breakdown
- glycogen phosphorylase coenzyme

red blood cell formation and function
- synthesis of heme

Immune function
- not clear

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13
Q

Amino acid that seratonin is synthesized from

A

tryptophan

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14
Q

How does B6 affect hormone function

A

PLP binds to steroid hormone receptors to decrease the effects

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15
Q

PLP role in glycogen breakdown

A

Coezyme for glycogen phosphorylase

- key enzyme converting glycogen to glucose (glycogenolysis)

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16
Q

PLP role in Red blood cell formation and function

A

Positive:
Coenzyme for synthesis of heme (part of hemoglobin)

Negative:
Pyridoxal (PL) and Pyridoxal Phosphate (PLP) can bind to hemoglobin molecule - affect pick of and release of O2 (affect not known)

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17
Q

PLP role in immune function

A
  • coenzyme for mobilization of single carbon functional groups
  • Serine OH-methyltransferase
  • synthesis DNA/RNA
  • Deficiency decrease IL-2, decreased lymphocyte proliferation

** not well known

18
Q

***Assessing Vitamin B6 status

A
  • **Load Tests:
  • Tryptophan load test
  • Methianine Load Test

Other:
4-Pyridoxic acid in urine
- absent in deficiency

19
Q

Why can’t we use B6 intake when assessing B6 status

A

Intake doesn’t consider the bioavailability

20
Q

Vit B6 deficiency

A
  1. Nervous system:
    - irritability, depression, confusion
    - sleeplessness
    - abnormal EEG patterns (measuring electro-activity around the scalp)
  2. Dermatitis, cheilosis, stomatitis
21
Q

Vit B6 deficiency similar to what other deficiency

A

Riboflavin

  • both needed in kynurenine pathway
  • riboflavin needed for B6 coenzyme form
22
Q

B6 Requirement affected by?

A

Protein intake
- B6 main role in amino acid metabolism

Oral contraceptives
Alcoholism
Pregnancy and lactation

  • last 2 affect almost everything
23
Q

B6 food sources

A

fortified cereals
meats
grains
legumes

24
Q

B6 loss in food caused by?

A

Milling

as with other B vitamins

25
Q

B6 drug interactions

A

High doses B6 can ‘decrease’ efficacy of:

  • Anti-TB meds (tuberculosis)
  • Anti-Convulsant meds (epilepsy)

B6 forms complexes with drugs, causing B6 deficiency

26
Q

B6 involved in what Health/Disease factors

A

CVD

  • homocysteine Hcy build up is a sign of CVD
  • PLP needed conversion Hcy to cysteine

Immune Function
- low B6 associated w impaired immune function (particularly in elderly)

Cognitive Function

  • Decline w low B6 (also folate and B12)
  • Memory?

Depression
- PLP-dependent neurotransmitter serotonin

PMS
-relieves symptoms

Others: Morning sickness, carpal tunnel, kidney stones

27
Q

Largest, most complex structure of the B vitamins?

A

B12

28
Q

Center of B12 structure

A

cobalt

29
Q

B12 also called

A

Cobalamin

30
Q

B12 structures

A

R group off of the centre cobalt

R=Methyl
- methyl-cobalamin

R=Adenosyl
- 5’-deoxyadenosyl-cobalamin

R=CN (synthetic form)
- Cyanocobalamin

*KNOW THESE

31
Q

B12 absorption

A

3 phase process:

  • gastric phase
  • luminal phase
  • mucosal phase

depends on pH and presence of receptors

32
Q

Intrinsic Factor (IF) and B12

A

key to B12 absorption

  • glycoprotein released to stomach by parietal cells
  • binds B12
  • allows passage into ileum
  • Ilium has receptor for IF-B12
33
Q

Gastric phase B12 absorption

A

1st phase (stomach)

Digests protein bound B12
Free-cobalamin binds R-proteins
- high affinity
- IF doesn’t bind at this point

34
Q

Luminal Phase B12 absorption

A

2nd phase (duodenum)

R-proteins digested and Free cobalamin, now combine with IF (released by parietal cells)

35
Q

Mucosal phase B12 absorption

A

3rd (final) phase (ileum)

IF-B12 bind receptors in the Ileum
Absorption occurs

36
Q

B12 metabolic role

A

Methyl Cobalamin:
mehtionine synthetase
- Hcy to methionine (also need folate)

Adenosyl Cobalamin:
methylmalonyl CoA mutase
- propionate catabolism
- propionate -> **methymalonyl CoA --> succinyl CoA
- enters TCA cycle

**methylmalonyl CoA (MMA) only way to measure metabolism

37
Q

Factors affecting B12 absorption

A

Atrophic Gastritis

  • decrease gastric acid
  • age related decrease in parietal cells

Decreased Intrinsic Factor
- age related decrease parietal cells

Pancreatic Insufficiency
- decreased protein absorption

38
Q

B12 deficiency

A

Pernicious Anemia

  • lack of IF
  • diagnosed with Schilling Test (radioactively labels cobalt)
  • B12 injection treatment (skips absorption)

Neurological problems

  • memory loss, demetia, weakness, tiredness
  • 7 years to develop
  • can be irreversible
39
Q

Urinary signs of B12 deficiency

A

elevated levels of

  • homocysteine
  • methymalonic acid***
40
Q

B12 defeciency / folate relation

A

Folate masks B12 deficiency

  • both folate and B12 deficiency cause macrocytic anemia
  • folate can correct the anemia of B12 deficiency but NOT neurological symptoms
41
Q

How “breath test” can asses B12 status`better

A
  • Examines rate of oxidation of 13C-propionate to 13CO2 in breath
  • C13 label on propionate is used and CO2 in breath is measured
  • B12 coenzyme role in propionate catabolism
42
Q

B12 food sources

A

Animal sources only

Some B12 synthesized by anaerobic microorganism (algae)

Nutrition 3330 (22 decks)

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