Vitamin B Family Tree - Group 1

Folate

Folate

Polyglutamate forms of folate are hydrozyled to monoglutamate forms prior to absorption.

PCFT (Protone Coupled Folate Transporter) is the main carrier of folate transportation to intenstine.

Folate binding proteins transport folate into most tissue cells and within cells.

Inside enterocytes, folate is converted into 5-methyl THF or formyl-THF.

In liver and other tissues, is converted to polyglutamate form to be a functional enzyme.

Tetahydrofolate

(THF)

Main Functions:

- Nucleotide Synthesis

- Carrier of actived one-carbon units to form THF derivatives.

NAD - nicotinamide

adenine dinucleotide

NADP- Nicotinamide adenine dinucleotide phosphate

Niacin

Absorbtion:

NAD and NADP hydrolized to nicotinamide

Nicotinic acid and nicotinamide absorbed in small intestine

Transportation:

In blood- Nicotinamide and nicotinic acid move across cell membranes by simple diffuison

In liver and other cells- NAD and NADP made from nicotinamide

Niacin

Thiamin

TDP/TPP is converted into free thiamin before absoprtion into the enterocyte

TDP- thiamin diphosphate

It is transported in the blood bound to albumin

It is taken up by the liver and converted back to TDP by thiamin pyrophosphokinase

TPP- thiamin pyrophosphate

Main Function

Thiamin

energy transformation: oxidative decarboxylation

a coenzyme for transketolase to synthesize pentoses and NADPH

Pantothenic Acid

Coenzyme A

Synthesized by pantothenic acid, cystenine, ATP in body

Absorbtion:

Coenzyme A, major form found in food, is hydrolyzed to pantothenic acid. It is absorbed via passive diffusion when bioavailability is high, however, depends on multivitamin carrier when concentration is low. It transport in blood freely.

Function:

Acetylation of protein, sugar, drugs

Acyl transfer reaction

Pantothenic

Acid

Riboflavin

Absorbtion- FAD and FMN in foods are hydrolized by phosphatases to free riboflavin.

Free form absorbed by either diffusion, carrier-mediated, or energy-dependent process

Transportation- free riboflavin transported in blood and converted to FAD and FMN via flavokinase and FAD synthase in cells

Greatest concentrations of FAD and FMN in the liver, kidney, and heart.

Riboflavin

FMN- flavin mononucleotide

FAD- flavin adenine dinucleotide

Main Functions:

Energy Transformation

ETC

TCA Cycle

Fatty Acid Oxidation

Reducing Enzymes

Biotin

Biotin can be synthesized by bacteria in the colon, but not at a high enough rate

Biotin

Absorption: Biotin is absorbed mostly in the small intestine, specifically the jejunum and ileum. This can be guided through either passive diffusion or carrier-facilitated diffusion.

Transport: The Na-dependent multivitamin transporter (SMVT) transports biotin for tissue uptake, the same transporter used by pantothenic acid.

Biotin

Vitamin B12

Adenosylcobalamin

In the doudenum, cobalamins are released from R-proteins, and bind to intrinsic factor (IF) complexes. In the ileum, B12 is absorbed via an IF receptor mediated process. B12 can re-enter the GI tract via bile and be recirculated (enterohepatic circulation).

B12 is transported in the blood via transcobalamin transport proteins: TC I,II & III.

B12 is required for Methionine Synthase (conversion of homocysteine to methionine, 5-methyl THF to THF), and L-methylmalonyl-CoA Mutase (conversion of L-methymalonyl-CoA to Succinyl-CoA)

Vitamin B12

Methylcobalamin

Vitamin B6

- B6 is stored in the body as pyridoxal phosphate, the phosphorylated forms must be dephosphorylated and the pool of free vitamin B6 is absorbed by passive diffusion, which are primarily absorbed in the jejunum.

- The liver is the main organ that takes up and metabolizes newly absorbed B6. In the blood, PLP binds to albumin in the serum and hemoglobin in red blood cells.

Functions:

- Reactions are involved in amino acid metabolism, which include transamination, decarboxylation, and synthesis.

- PLP is required for glycogen degradation and biosynthesis of sphingolipids, neurotransmitters, and niacin.

PLP

Vitamin B6