Vitamin B6

vitamers

different forms of a vitamin

List the different vitamers of B6

Plant foods: pyridoxine (PN); pyridoxine phosphate (PNP)

Animal foods: pyridoxal (PL), pyridoxal phosphate (PLP); pyridoxamine (PM), pyridoxamine phosphate (PMP)

Sources of vitamin B6

beef, pork, chicken, fish, oysters

fortified cereals

bananas and potatoes

navy beans

RDA for vitamin B6

Men and women 19-50 years: 1.3mg/day

Digestion of B6

dephosphorylation of PNP, PLP, or PMP to form either PN, PL, or PM respectively

achieved by phosphatases

absorption of B6

primarily in the jejunum by passive transport and then released into the systemic portal blood

How and where is vitamin B6 stored?

inside cells, B6 is phosphorylated by kinases to prevent diffusion outside of the cell and is stored by proteins to prevent hydrolysis

major storage site: muscle

How is vitamin B6 excreted?

in the urine as 4-pyridoxic acid

Explain transanimation reactions

an amine group is donated from an amino acid to PLP (attached to a aminotransferase). This converts PLP to PMP and creates a new alpha keto acid. PMP then donates the amine group to a different alpha keto acid which produces a new amino acid and converts PMP back to PLP

Why are transanimation reactions important?

they are needed to synthesize non essential amino acids

UL of B6

100mg/day

Vitamin B6 deficiency

affects the central and peripheral nervous system and can cause neuroplasty and microcytic hypochromic anemia

Who is at risk of vitamin B6 deficiency?

older adults due to poor intake+ degradation of the vitamin

alcohol abuse (impaire PLP formation))

certain drugs

systemic inflammation (increases vitamin catabolism)

renal dialysis, malabsorption conditions, pre-eclampsia

indicators of B6 status

Best indicator: plasma PLP

short-term indicator: urinary 4-pyridoxic acid

Xanthurenic acid following tryptophan loading

Explain how urine Xanthurenic acid can indicate a vitamin B6 deficiency

In order to convert tryptophan to niacin, vitamin B6 is needed as a coenzyme. When there is a deficiency, xanthurenic acid is made instead and is excreted in the urine