Pyroxidine (B6)

Question 1

3 Vitamers

Answer 1

Aldehyde = Pyridoxial (PL)
Amine = pyridoxamine (PM)
Alcohol = pyridoxine (PN)

Question 2

Active form and reactive groups

Answer 2

PLP
- Carbonyl group for AA metabolism
- Phosphate group for glycogen phosphorylase
- Activation is reversible via PL kinase

Question 3

Primary role of pyridoxine

Answer 3

Amino acid metabolism (transamination, decarboxylation, transulferation, deamination, phosphorylase and protein structure)

Question 4

4 roles:

Answer 4

• AA metabolism
• Trp metabolism
• heme synthesis
• glycogen breakdown

Question 5

How is B6 involved in transamination

Answer 5

The amino group binds to PLP, making PMP, and then transfers to the a-keto acid

Question 6

How is B6 involved in decarboxylation

Answer 6

PLP decarboxylates AA into a Schiff base, which is then converted into an amine. AA decarboxylation is used for AA synthesis of hormones and neurotransmitters (amines).

Question 7

Why is B6 important for niacin status?

Answer 7

Conversion of Trp to niacin requires B6 for the enzyme kynureninase.

Question 8

How is B6 involved in heme synthesis?

Answer 8

PLP required in rate limiting step in heme biosynthesis

Question 9

Main storage form of B6

Answer 9

PLP - used for metabolic trapping

Question 10

B6 metabolism

Answer 10

1. Break down protein - release cofactor
   
   2. Dephosphorylate - break it down to its vitamers (3)
   3. Transport to the enterocyte - some will be used some will be transport
      ○ Transport through albumin to liver
   4. Some will get oxidized in the liver (CANNOT be used)
   5. Gets transported again - phosphorylated and stored or used

Question 11

Storage location

Answer 11

80-90% in muscle (glycogen phosphorylase); 10% in liver

Question 12

Signs of B6 deficiency

Answer 12

• Hematological: microcytic anemia, hyper Hcy
• Nervous system: ataxia, depression, convulsions
• Skin: dermatitis, lesions

Question 13

How is B6 status determined

Answer 13

• Plasma PLP and urinary excretion of pyridoxic acid
• Activity of dependent enzymes
• Trp load - excretion of catabolites
• Met load test (plasma and urinary Hcy and cystathionine)

Question 14

Requirements

Answer 14

M and F: 1.3mg, UL: 100mg/day
- Requirements related to protein intake

Question 15

Forms found in plant vs animal vs supplement

Answer 15

Animal: PLP and PMP
Plant: PN
Supplements and fortified: PN

Question 16

Bioavailability in supplement vs food

Answer 16

Supplements: >90%
Food: ~75% (PN-glycoside from plant is poorly used; PM can be inactivated through reaction with carbonyl group of red sugards and ascorbic acid)