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nutr 3330 midterm > Vit B6 B12 > Flashcards

Vit B6 B12 Flashcards

1
Q

is Vit B6 phosphorylated or unphosphorylated in foods

A

phosphorylated

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2
Q

what is the coenzyme form of Vitamin B6

A

pyridoxal Phosphate (PLP)

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3
Q

what vitamin is needed to convert pyridoxine to PLP

A

riboflavin

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4
Q

what are the metabolic role of Vit B6

A 
Amino acid metabolism
nervous system
hormone function
glycogen breakdown
red blood cell formation and function
immune function
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5
Q

describe the metabolic role of Vit B6

A
  • transamination
  • R-group interconversion
  • decarboxylations
  • recall typrotphan metabolism… synthesis of niacin…kynurenine pathway
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6
Q

Schiff Base

A

allows PLP to effectively facilitate amino acids metabolism
PLP binds to enzyme
link formed between PLP aldehyde group and enzyme amino group, forms an IMINE group

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7
Q

Vit B6 in nervous system

A
  • synthesis of neurotransmitters involvve PLP-dependent enzymes
  • serotonin is synthesized from tryptophan
  • Vit B6 deficiency… neurological problems
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8
Q

Vit B6 in hormone function

A
  • PLP is not a hormone but can bind to steroid hormone receptors
  • competes with the hormone, inhibits binding and makes it less effective
  • could be useful in blocking hormones that are related to diseases
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9
Q

vit B6 in glycogen breakdown

A
  • PLP involved in glycolysis
  • coenzyme for glycogen phosphorylase
  • key enzyme in conversion of glycogen to glucose
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10
Q

vit B6 in red blood cell formation and function

A

PLP involved in synthesis of heme

  • acts as coenzyme
  • allows RBC to transport oxygen throughout body

Pyridoxal (PL) and PLP are able to bind to hemoglobin molecule

affect its ability to pick up and release oxygen

impact on normal oxygen delivery to tissues is not known

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11
Q

B6 in immune function

A

one carbon metabolism/transfer of one carbon units

serine OH-methyltranferase

synthesis of nucleic acids

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12
Q

assessing Vit B6 statis

A

Load tests (tryptophan and methionine)

4-pyridoxic acid

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13
Q

tryptophan load test

A
  • impaired conversion to niacin

- build up of urinary kynurenic acid xanthurenic acid; metabolites derived from kynurenine pathway

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14
Q

methionine load test

A
  • 2 PLP-dependent steps in MET metabolism
  • methionine–> homocysteine–> cysteine impaired
  • increased homocysteins

need B6 to go from homocysteine to cysteine so if B6 is impaired, there will be a build up of homocysteine

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15
Q

assessing Vit B6 status:

4-pyridoxic acid

A
  • major urinary metabolite

- absent with deficiency

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16
Q

B6 deficiency

A

b6 deficiencies are not usually specific

  • nervous system (irritability, depression, confusion, sleeplessness, abnormal EEG patterns)
  • dermatitis; cheilosis, stomatitis
  • similar to riboflavin deficiency
17
Q

why is a B6 deficiency similar to a riboflavin deficiency?

A

if there is a B6 problem, we could have a problem with riboflavin, since we need B6 to convert riboflavin to its coenzyme form

18
Q

Vit B6 requirement

A
  • requirement affected by protein intake
    • oral contraceptives
    • alcoholism
    • increase in pregnancy and lactation
19
Q

B6/drug interactions

A
  • anti-TB meds
  • anti-consultant meds
  • high doses of B6 can decrease efficacy of these drugs
  • need to pay attention to balance
  • form complexes with Vit B6, reducing the efficacy of drug and creating a vit B6 deficiency
20
Q

B6 health/disease

A
  • CVD
    • relation to homocysteine (Hcy)
    • PLP needed for one Hcy pathways
  • immune function
    • association between low B6 and impaired immune function, especially in elderly
  • congnitive function
    • role in neurotransmitters
  • depression
    • PLP-dependent NT serotonin

PMS
-vit B6 used to relieve PMS

OCA side effects (oral contraceptive)

21
Q

which B vitamin is the largest and most complex structure

A

B12

cobalmin

22
Q

what does Vit B12 have in the center of its structure

A

cobalt

23
Q

study reminder

A

need to recognize B12 structure

24
Q

B12 absorption

A
  • involves 3 phases

- stepwise process that depends on pH and presence of receptors

25
Q

what are the 3 phases of B12 absorption

A 
gastric phase (stomach)
luminal phase (SI)
mucosal phase (LI)
26
Q

Intrinsic factor (IF)

A 
key to B12 absorption
glycoprotein release into stomach by parietal cells
binds to B12
allows passage into the ileum
ileum has receptor for IF-B12
absorption occurs
27
Q

gastric phase of B12 absorption

A
  • digestion of protein bound B12 (cobalamin)
  • free-cobalamin now binds with R-proteins
  • IF is synthesized and released by partietal cells but does not bind cobalamin at this point
28
Q

Luminal phase of B12 absorption

A

-R-proteins are digested adn free cobalamin again, and can now combine with IF

29
Q

mucosal phase of B12 absorption

A

Receptors for IF-B12 complex in the ileum…absorption occurs

30
Q

what are the two coenzyme forms of B12

A

methyl cobalamin

adenosyl cobalamin

31
Q

what is the role of methyl cobalamin

A
  • methionine synthetase
    • methionine synthesis
    • Hcy to methionine
    • also needs folate
32
Q

what is the rols of adenosyl cobalamin

A

methylmalonyl CoA mutase

  • propionate catabolism
  • propionate to methlmalonyl CoA to succinyl CoA
  • entry to TCA cycle
33
Q

B12 malabsorption

A

atrophic gastritis

  • dec gastric acid
  • age related decrease in parietal cells that secrete HCl therefore less acid

deacreased intrinsic factor
-age related

pancreatic insufficiency
-decreased protein digestion

34
Q

B12 deficiency

A

elevated urinary concentrations of homocysteine and methylmalonic acid

pernicious anemia (changes to red blood cells)

  • lack of IF; lack of absorption
  • diagnosed with Schilling test…cobalt would be labelled

neurological problems
-slow onset

35
Q

what effect does folate have on a vitamin B12 deficiency

A

it masks it.

It can rectify anemia of B12 deficiency but not neurological symptoms

36
Q

what could you measure that would specifically tell you there is a B12 deficiency

A

methylmolonyl CoA

37
Q

food sources of B12

A

animal products only (meat, dairy, fish)

nutr 3330 midterm (13 decks)

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