WATER SOLUBLE VITAMINS Vitamin B-complex Dr. Shivani Pandey, Department of Biochemistry, K.G. Medical University, Lucknow

Thiamine Dr. Shivani Pandey, Department of Biochemistry

Dr. Shivani Pandey, Department of Biochemistry

Dr. Shivani Pandey, Department of Biochemistry

Dr. Shivani Pandey, Department of Biochemistry

Dr. Shivani Pandey, Department of Biochemistry

Dr. Shivani Pandey, Department of Biochemistry

Dr. Shivani Pandey, Department of Biochemistry

Dr. Shivani Pandey, Department of Biochemistry

Dr. Shivani Pandey, Department of Biochemistry

Dr. Shivani Pandey, Department of Biochemistry

Dr. Shivani Pandey, Department of Biochemistry

Dr. Shivani Pandey, Department of Biochemistry

Dr. Shivani Pandey, Department of Biochemistry

Dr. Shivani Pandey, Department of Biochemistry

Dr. Shivani Pandey, Department of Biochemistry

Dr. Shivani Pandey, Department of Biochemistry

Dr. Shivani Pandey, Department of Biochemistry

Dr. Shivani Pandey, Department of Biochemistry

Dr. Shivani Pandey, Department of Biochemistry

Dr. Shivani Pandey, Department of Biochemistry

Dr. Shivani Pandey, Department of Biochemistry

Dr. Shivani Pandey, Department of Biochemistry

Dr. Shivani Pandey, Department of Biochemistry

Dr. Shivani Pandey, Department of Biochemistry

Dr. Shivani Pandey, Department of Biochemistry

Dr. Shivani Pandey, Department of Biochemistry

Dr. Shivani Pandey, Department of Biochemistry

Dr. Shivani Pandey, Department of Biochemistry

Dr. Shivani Pandey, Department of Biochemistry

Dr. Shivani Pandey, Department of Biochemistry

Dr. Shivani Pandey, Department of Biochemistry

Dr. Shivani Pandey, Department of Biochemistry

Dr. Shivani Pandey, Department of Biochemistry

Dr. Shivani Pandey, Department of Biochemistry

Dr. Shivani Pandey, Department of Biochemistry

Dr. Shivani Pandey, Department of Biochemistry

Dr. Shivani Pandey, Department of Biochemistry

Dr. Shivani Pandey, Department of Biochemistry

Dr. Shivani Pandey, Department of Biochemistry

Dr. Shivani Pandey, Department of Biochemistry

Dr. Shivani Pandey, Department of Biochemistry

Riboflavin Dr. Shivani Pandey, Department of Biochemistry

Dr. Shivani Pandey, Department of Biochemistry

Dr. Shivani Pandey, Department of Biochemistry

Dr. Shivani Pandey, Department of Biochemistry

Dr. Shivani Pandey, Department of Biochemistry

Dr. Shivani Pandey, Department of Biochemistry

Dr. Shivani Pandey, Department of Biochemistry

Dr. Shivani Pandey, Department of Biochemistry

Dr. Shivani Pandey, Department of Biochemistry

Dr. Shivani Pandey, Department of Biochemistry

Dr. Shivani Pandey, Department of Biochemistry

Dr. Shivani Pandey, Department of Biochemistry

Dr. Shivani Pandey, Department of Biochemistry

Dr. Shivani Pandey, Department of Biochemistry

Dr. Shivani Pandey, Department of Biochemistry

Dr. Shivani Pandey, Department of Biochemistry

Dr. Shivani Pandey, Department of Biochemistry

Dr. Shivani Pandey, Department of Biochemistry

Dr. Shivani Pandey, Department of Biochemistry

Dr. Shivani Pandey, Department of Biochemistry

Dr. Shivani Pandey, Department of Biochemistry

Dr. Shivani Pandey, Department of Biochemistry

Dr. Shivani Pandey, Department of Biochemistry

Dr. Shivani Pandey, Department of Biochemistry

Dr. Shivani Pandey, Department of Biochemistry

Dr. Shivani Pandey, Department of Biochemistry

Pyridoxine Dr. Shivani Pandey, Department of Biochemistry, K.G. Medical University, Lucknow

PYRIDOXINE (vitamin B6) Pyridoxal (PL)

Pyridoxamine (PM)

Pyridoxine or Pyridoxol (PN)

Each of these forms can be phosphorylated at position 5 to form: PLP, PMP & PNP Dr. Shivani Pandey, Department of Biochemistry

Active form Pyridoxal phosphate (PLP)

• Active functional form is pyridoxal phosphate (PLP) and pyridoxamine phosphate (PMP). • For absorption, the “phosphorylated” form must be hydrolyzed to “dephosphorylated” form by the enzyme alkaline phosphatase in the intestine. • In the portal vein Vit B6 is present as PL, PM, PN. • In the liver they are converted back to phosphorylated forms. This conversion is catalyzed by the ATP requiring enzyme, pyridoxal kinase.

• PLP and PL account for 90% of the total B6 in the blood. • In the blood B6 is transported both in the plasma and the RBCs. • In the blood PLP is hydrolyzed to PL because only free PL gets inside the cells. • In muscle and other tissues, PL is converted back to PLP by a reversible reaction with the help of alkaline phosphatase and pyridoxal kinase. Dr. Shivani Pandey, Department of Biochemistry

Functions FUNCTIONS: B6 is involved in: Amino acid metabolism Transamination reactions required for the synthesis and catabolism of the amino acids. Decarboxylation reactions. Breakdown of glycogen Glycogenolysis (cofactor for glycogen phosphorylase). 80-90% of body vit B6 is present in the muscles, most of it in PLP (coenzyme) form bound to glycogen phosphorylase. Only 1 mol or less is present in the blood, Synthesis of epinephrine (adrenaline) and norepinephrine (noradrenaline) Synthesis of niacin (vitamin B3) from the amino acid tryptophan.

Dr. Shivani Pandey, Department of Biochemistry

Covalent bonds of -amino acids made labile by their binding to PLP-containing enzyme In the reactions of amino acid metabolism, the formyl (CHO) group of PLP condenses with -NH2 group of an amino acid and forms a Schiffs base. This linkage weakens or labilizes all the bounds around the -carbon of the amino acid.

The specific bond of an amino acid that is broken depends on the particular enzyme to which PLP is attached.

Dr. Shivani Pandey, Department of Biochemistry

Mechanism of catalyzed reaction

Dr. Shivani Pandey, Department of Biochemistry

Deficiency 

Food sources:   



Requirements: 

 



The requirement for vitamin B6 in the diet is proportional to the level of protein consumption ranging from 1.4 - 2.0 mg/day for a normal adult. During pregnancy and lactation the requirement for vitamin B6 increases approximately 0.6 mg/day.

TOXICITIES: 



In animal foods major forms are PL and and PM along with their phosphorylated forms. In plants PN. Bananas, beans, lentils, walnuts, salmon, chicken, beef, whole grain breads and cereals, soybeans, liver, eggs, dairy products are excellent sources.

Megadoses of B6 (daily doses of >500mg) are used to treat pms symptoms. They can cause neurotoxicity and photosensitivity in some individuals.

Deficiencies: are rare and usually are related to an overall deficiency of all the B-complex vitamins. Certain drugs form complexes with PL and PLP  

Penicillamine (used to treat rheumatoid arthritis and cystinurias). Isoniazid (the hydrazide derivative of isonicotinic acid) is the primary drug for chemotherapy of tuberculosis. Dr. Shivani Pandey, Department of Biochemistry

Biotin Dr. Shivani Pandey, Department of Biochemistry

BIOTIN It is sometimes called vitamin H and also coenzyme R. 

  

Biotin is relatively small, bicyclic (two-ring) compound formed from a tetrahydrothiophene (thiophene) ring

,

and a second ring, which contains a ureido group. The thiophene ring also has a valeric acid side chain. Although eight different stereoisomers of biotin exist, only one stereoisomer is found naturally and to have biological activity as a coenzyme. It is called d-(+)-biotin, D-biotin or simply biotin. Dr. Shivani Pandey, Department of Biochemistry

Holocarboxylase

In humans, the four holocarboxylases are : acetyl-CoA carboxylase, propionyl-CoA carboxylase, pyruvate carboxylase and betamethylcrotonyl-CoA carboxylase. Biotin is chemically bonded in each of these enzymes via an amide linkage between the carboxyl group of the valeric acid side-chain in biotin and the epsilon-amino group of the lysine residue in the apocarboxylase. The enzyme that catalyzes the formation of this covalent bond is called holocarboxylase synthetase. Dr. Shivani Pandey, Department of Biochemistry

Biotin Cycle Biotin cycle: the chain of chemical reactions involved in the use and reuse of the vitamin biotin. One important role of biotinidase is:

1. To separate or free biotin from proteins to which it is bound in foods. Biotin in its free form can then be used by the body. 2. Biotinidase lets the body recycle or reuse the biotin over and over again so that we do not need to consume large amounts of this vitamin in our diets. •Within cells, the carboxylases (pyruvate carboxylase, acetyl-CoA carboxylase, methycrotonyl-CoA carboxylase, propionyl-CoA carboxylase) are biotinylated via holocarboxylase synthetase. Biotin and apocarboxylases are the substrates. ATP and magnesium also participate in the reaction. Biotinidase deficiency is a treatable, inherited metabolic disorder in which the body cannot process the vitamin biotin in a normal manner.

Dr. Shivani Pandey, Department of Biochemistry

Functions



Coenzyme involving CO2 transfer  acetyl

CoA to malonyl CoA  Propionyl CoA to methylmalonyl CoA  Pyruvate to oxaloacetate 

Deficiency  Fatty

liver and kidney syndrome, a fatal metabolic disorder in chicks and turkey poults



Raw egg white (avidin) can block absorption

Dr. Shivani Pandey, Department of Biochemistry

Biotin (functions) 

Coenzyme for several reactions involving CO2 fixation into various compounds e.g. Acetyl CoA to malonyl CoA (acetyl CoA carboxylase) - initial step in de novo fatty acid synthesis.

Pyruvate to oxaloacetate (pyruvate carboxylase) Propionyl CoA to methylmalonyl CoA (propionyl CoA carboxylase) Dr. Shivani Pandey, Department of Biochemistry

Deficiency symptoms 

Rare because of widespread distribution in plant and animal food and significant lower gut synthesis. 



Can be induced by eating raw egg white 





Sources  Yeast, rice, soybeans, peanuts, fish (herring and mackerel), mushrooms and bananas, safflower meal, liver and milk are rich sources. The fact is that nature created the egg in such a way that its yolk is very rich in biotin. One of the highest concentration in nature. Eat the egg whole together with the egg white and you will be fine. Egg whites contain a glycoprotein called "avidin" which binds biotin - one of the B vitamins - very effectively. The cooking process deactivates the avidin in the egg, much the same way it deactivates every other protein in the egg white.

Biotin deficiency is chief cause of fatty liver and kidney syndrome.

This baby developed severe biotin deficiency during intravenous feeding without biotin.

Aajonus Vonderplanitz, in his book “We Want to live” is a strong proponent of raw eggs.

Dr. Shivani Pandey, Department of Biochemistry

How Biotin Works

1- Biotin carrier protein 2- Biotin carboxylase 3- Transcarboxylase Dr. Shivani Pandey, Department of Biochemistry

Folic Acid Dr. Shivani Pandey, Department of Biochemistry

FOLIC ACID (folacin) • Folacin includes several derivatives of folic acid (monopteroylglutamic acid). • Folic acid is obtained primarily from yeasts and leafy vegetables as well as animal liver. Animals cannot synthesize PABA nor attach glutamate residues to pteroic acid, thus, requiring folate intake in the diet.

“Microorganisms Only can synthesize Folacin” Sulphonamides and antibiotics block PABA incorporation by competitive inhibition Dr. Shivani Pandey, Department of Biochemistry

Structure

Folic acid exists in a polyglutamate form. Intestinal mucosal cells remove some of the glutamate residues through the action of the lysosomal enzyme, conjugase. Dr. Shivani Pandey, Department of Biochemistry

Active functional form is: Tetrahydrafolic acid (THF). Humans and microorganisms: Folic acid is reduced within cells (principally in the liver where it is stored) to tetrahydrofolate (THF or H4folate) through the action of folate reductase [or dihydrofolate reductase (DHFR) ] which is an NADPH-requiring enzyme. Dr. Shivani Pandey, Department of Biochemistry

Active center (N5 and N10)

Dr. Shivani Pandey, Department of Biochemistry

• Active center of tetrahydrofolate (THF). The N5 position is the site of attachment of methyl and formimino groups, the N10 the site for attachment of formyl group and that both N5 and N10 bridge the methylene and methenyl groups. Dr. Shivani Pandey, Department of Biochemistry

Folate conversions

Carrier of one-carbon (e.g. methyl) groups The one-carbon units are added to, or removed from, metabolites such as: • histidine • serine • methionine • purines. Dr. Shivani Pandey, Department of Biochemistry

Functions •

Role of N5,N10-methylene-THF in dTMP synthesis is the most metabolically significant function for this vitamin.

•

Vitamin B12 and N5-methyl-THF in the conversion of homocysteine to methionine is important in helping cells to regenerate needed THF.

Dr. Shivani Pandey, Department of Biochemistry

Participation of H4folate in dTMP synthesis ______Deoxyuridine______________

________Deoxythymidine

____Monophosphate (dUMP)_______________Monophosphate (dTMP)_______

Dr. Shivani Pandey, Department of Biochemistry

ATP

Methyl Cycle

Methionine

S-Adenosylmethionine

Methyl-B12

Methyl group acceptor Homocysteine

S-Adenosylhomocysteine (SAH)

5 Methyl-THF One-carbon Pool Adenosine Dr. Shivani Pandey, Department of Biochemistry

Deficiency symptoms Deficiency is rare due to the adequate presence of folate in food. Deficiency can occur when there is: 1. Poor dietary habits as those of chronic alcoholics. 2. Impaired absorption or metabolism • Certain drugs such as anticonvulsants and oral contraceptives and methotrxate can impair the absorption of folate. 3. An increased demand for the vitamin. • Pregnancy • Folate will nearly double by the third trimester of pregnancy.

• Identical to those for vitamin B12 deficiency: • Effect of folate deficiency on cellular processes is upon DNA synthesis.

– Impairment in dTMP synthesis and purine synthesis – Cell cycle arrest in S-phase of rapidly proliferating cells, especially hematopoietic cells.

• The result is megaloblastic leukemia as for vitamin B12 deficiency.

– The inability to synthesize DNA during erythrocyte maturation leads to abnormally large erythrocytes termed macrocytic anemia.

• Deficiency during pregnancy can cause neural tube defects such as spina bifidia. Dr. Shivani Pandey, Department of Biochemistry

What are neural tube defects? • neural tube defects (NTDs) are birth defects that occur early in pregnancy – often before a woman knows she is pregnant

• neural tube grows to become baby’s spinal cord, spine, brain and skull

Dr. Shivani Pandey, Department of Biochemistry

The neural tube forms in the embryo and then closes (between the 2nd and 4th week of gestation) A neural tube defect occurs when the neural tube fails to close properly The two most common NTDs are anencephaly and spina bifida Dr. Shivani Pandey, Department of Biochemistry

Dr. Shivani Pandey, Department of Biochemistry

Which NTDS are most common? • Spina Bifida – a condition that results when the lower part of the neural tube fails to develop properly

Occult a Meningocele

Myelomeningocele

• Anencephaly – a fatal condition in which the upper end of the neural tube fails to close Dr. Shivani Pandey, Department of Biochemistry

Neural tube defects Spina Bifida

Anencephaly

Dr. Shivani Pandey, Department of Biochemistry

How Can NTDs be Prevented? • All women of childbearing age should receive 0.4 mg (400 micrograms) of folic acid daily prior to conception of planned or unplanned pregnancies and continue thru 1st trimester • Women with a history of NTD and should receive daily supplementation of 4 mg (4000 micrograms) of folic acid starting three months prior to conception and continuing thru the 1st trimester Dr. Shivani Pandey, Department of Biochemistry

Vitamin B12

Dr. Shivani Pandey, Department of Biochemistry

VITAMIN B12 (cobalamin) •

Vitamin B12, is also called cobalamin, cyanocobalamin and hydroxycobalamin.

•

It is built from :

• • •

1. A nucleotide and 2. A complex tetrapyrrol ring structure (corrin ring) 3. A cobalt ion in the center. 4. A R- group

When R is cyanide (CN), vitamin B12 takes the form of cyanocobalamin. In hydroxycobalamin, R equals the hydroxyl group (-OH). In the coenzyme forms of vitamin B12, – –

•

R equals an adenosyl group in adenosylcobalamin. R equals a methyl (-CH3) group in methylcobalamin.

Vitamin B12 is synthesized exclusively by microorganisms (bacteria, fungi and algae) and not by animals and is found in the liver of animals bound to protein as methycobalamin or 5'deoxyadenosylcobalamin.

Dr. Shivani Pandey, Department of Biochemistry

• Known as the "red" vitamin because it exists as a dark red crystalline compound, Vitamin B12 is unique in that it is the only vitamin to contain cobalt (Co3+) metal ion, which, gives it the red color. • The vitamin must be hydrolyzed from protein in order to be active. • Intrinsic factor, a protein secreted by parietal cells of the stomach, carries it to the ileum where it is absorbed. • It is transported to the liver and other tissues in the blood bound to transcobalamin II. • It is stored in the liver attached to transcobalamin I. – It is released into the cell as Hydroxocobalamin (see the next slide)

Dorothy Crowfoot Hodgkin (1910-1994)

• In the cytosol it is converted to methylcobalamin. • Or it can enter mitochondria and be converted to 5’-deoxyadenosyl cobalamin.

Dr. Stadtman in her lab Dr. Shivani Pandey, Department of Biochemistry

In the cytosol

In mitochondria

Dr. Shivani Pandey, Department of Biochemistry

Functions •

Only two reactions in the body require vitamin B12 as a cofactor: 1. During the catabolism of fatty acids with an odd number of carbon atoms and the amino acids valine, isoleucine and threonine the resultant propionyl-CoA is converted to succinyl-CoA for oxidation in the TCA cycle. – methylmalonyl-CoA mutase, requires vitamin B12 as a cofactor in the conversion of methylmalonyl-CoA to succinyl-CoA. – 5'-deoxyadenosine derivative of cobalamin is required for this reaction

2. The second reaction catalyzed by methionine synthase converts homocysteine to methionine – This reaction results in the transfer of the methyl group from N5methyltetrahydrofolate to hydroxycobalamin generating tetrahydrofolate and methylcobalamin during the process of the conversion. Dr. Shivani Pandey, Department of Biochemistry

Methionine and Folate cycles are interrelated Methionine cycle Folate cycle

Methionine

SAM

THF CH2-THF

MS

Methyl acceptor

methyl transferases

B12

CH3-THF

CH3-

Homocysteine

Methyl acceptor

SAH

CBS B6

cystathionine

Transulfuration pathway

B6

cysteine Dr. Shivani Pandey, Department of Biochemistry

Deficiency symptoms • Pernicious anemia in humans (inability to absorb B12 because of lack of gastric intrinsic factor). • Neurological disorders due to progressive demyelination of nerve cells. – This results from increase in methylmalonyl-CoA. – Methylmalonyl-CoA is a competitive inhibitor of malonyl-CoA in fatty acid biosynthesis. – Can substitute malonyl-CoA in any fatty acid biosynthesis and create branched-chain fatty acid altering the architecture of normal membrane structure of nerve cells.

• Sources

– Synthesized only by microorganisms, so traces only are present in plants; liver is a rich source. – B12 is found in organ and muscle meats, fish, shellfish, dairy products, eggs and in fortified foods like breakfast cereals.

Dr. Shivani Pandey, Department of Biochemistry