4 B6 and B12 Flashcards Preview

Nutrition 3330 > 4 B6 and B12 > Flashcards

Flashcards in 4 B6 and B12 Deck (42):
1

6 related compounds of B6

pyridoxal, pyridoxine, pyridoxamine
- and their phosphates

2

B6 phosphorylated in..

foods

3

B6's phosphate removed by

intestinal enzymes

4

B6 absorption

well absorbed passively

5

Process that occurs when B6 is absorbed by tissues

re-phosphorylated in tissue

6

Urinary excretion metabolite of B6

4-pyridoxic acid

7

B6 coezyme form

pyridoxal phosphate (PLP)

8

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

riboflavin

9

PLP

pyridoxal phosphate
- coenzyme of B6
- over 100 PLP dependent enzymes
- amino acid metabolism

10

Primary role of B6

*amino acid metabolism
- Intermediary metabolism (GNG)
- Tryptophan metabolism
- synthesis of niacin (ribo also needed - kyneurine pathway)

11

Schiff Base

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'

12

B6 roles in metabolism

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

13

Amino acid that seratonin is synthesized from

tryptophan

14

How does B6 affect hormone function

PLP binds to steroid hormone receptors to decrease the effects

15

PLP role in glycogen breakdown

Coezyme for glycogen phosphorylase
- key enzyme converting glycogen to glucose (glycogenolysis)

16

PLP role in Red blood cell formation and function

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)

17

PLP role in immune function

- 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

***Assessing Vitamin B6 status

***Load Tests:
- Tryptophan load test
- Methianine Load Test

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

19

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

Intake doesn't consider the bioavailability

20

Vit B6 deficiency

1.Nervous system:
- irritability, depression, confusion
- sleeplessness
- abnormal EEG patterns (measuring electro-activity around the scalp)

2. Dermatitis, cheilosis, stomatitis

21

Vit B6 deficiency similar to what other deficiency

Riboflavin
- both needed in kynurenine pathway
- riboflavin needed for B6 coenzyme form

22

B6 Requirement affected by?

Protein intake
- B6 main role in amino acid metabolism

Oral contraceptives
Alcoholism
Pregnancy and lactation

* last 2 affect almost everything

23

B6 food sources

fortified cereals
meats
grains
legumes

24

B6 loss in food caused by?

Milling
(as with other B vitamins)

25

B6 drug interactions

High doses B6 can 'decrease' efficacy of:
- Anti-TB meds (tuberculosis)
- Anti-Convulsant meds (epilepsy)

B6 forms complexes with drugs, causing B6 deficiency

26

B6 involved in what Health/Disease factors

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

Largest, most complex structure of the B vitamins?

B12

28

Center of B12 structure

cobalt

29

B12 also called

Cobalamin

30

B12 structures

R group off of the centre cobalt

R=Methyl
- methyl-cobalamin

R=Adenosyl
- 5'-deoxyadenosyl-cobalamin

R=CN (synthetic form)
- Cyanocobalamin

*KNOW THESE

31

B12 absorption

3 phase process:
- gastric phase
- luminal phase
- mucosal phase

depends on pH and presence of receptors

32

Intrinsic Factor (IF) and B12

key to B12 absorption
- glycoprotein released to stomach by parietal cells
- binds B12
- allows passage into ileum
- Ilium has receptor for IF-B12

33

Gastric phase B12 absorption

1st phase (stomach)

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

34

Luminal Phase B12 absorption

2nd phase (duodenum)

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

35

Mucosal phase B12 absorption

3rd (final) phase (ileum)

IF-B12 bind receptors in the Ileum
Absorption occurs

36

B12 metabolic role

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

Factors affecting B12 absorption

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

B12 deficiency

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

Urinary signs of B12 deficiency

elevated levels of
-homocysteine
-methymalonic acid***

40

B12 defeciency / folate relation

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

How "breath test" can asses B12 status`better

-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

B12 food sources

Animal sources only

Some B12 synthesized by anaerobic microorganism (algae)