Biochemisrty

This presentation deals with Thiamine Pyrophosphate (TPP), Pyridoxal Phosphate (PLP) and Coenzyme- A .
A brief description about Vitamins and Co enzymes. Then synthesis and application of PLP, TTP and Co-enzyme A

1. THYAMINE PHOSPHATE (TPP), PYRODOXYL PHOSPHATE (PLP) & Coenzyme-A BY: SUCHITTA . U

2. VITAMINS The lipid-soluble vitamins are a polar hydrophobic compounds. They are transported in the blood, like any other apolar lipid, in lipoproteins or attached to specific binding proteins. The water-soluble vitamins comprise the B complex and vitamin C and function as enzyme cofactors. Lipid-soluble vitamins Vitamin A Vitamin D Vitamin E Vitamin K Water-soluble vitamins Vitamin C Vitamin B

3. Vitamin Functions Deficiency Disease B1 Thiamine Coenzyme in pyruvate and ketoglutarate dehydrogenase Beri beri , CNS lesions B2 Riboflavin Coenzyme in oxidation and reduction reaction; prosthetic group of flavoprotiens Lesions on corner of mouth, lips, and tongue; seborrheic dermititis Niacin, Nicotinic acid, nicotinamide Coenzyme in oxidation and reduction reaction; function al part of NAD and NADP Pellagra B6 Pyridoxin , Pyridoxal, Pyridoxamine Coenzyme in transamination and decarboxylation of amino acids Disorders of amino acids metabolic convulsions Folic acid Coenzyme in transfer of one carbon fragments Megaloblastic anemia B12 Cobalamin Coenzyme in transfer of one carbon fragments and metabolism of folic acids Pernicious anemia Pantothenic acid Functional part of CoA and acyl carrier protein: fatty acid synthesis

4. CO-factor A small non protein molecules that is bound (tightly or loosely) to an enzyme and is required for catalysis

5. Pyridoxal phosphate (PLP)

6. Pyridoxal phosphate (PLP) VITAMIN B 6 Six compounds have vitamin B6 activity: PYRIDOXINE, PYRIDOXAL, PYRIDOXAMINE and their 5’- phosphates Active coenzyme is pyridoxal 5’- phosphate It is important in amino acids, glycogen metabolism and in steroid hormone action. 80% of the body’s total volume - pyridoxal phosphate in muscles (glycogen metabolism) PLP was first discovered during mid forties as the co-factor for the transamination reactions PLP is biologically active form of vitamin B6

7. PLP Amino acid metabolism Transamination Decarboxylation Cofactor of glycogen phosphorylase Steroid hormone action PLP removes hormone receptor complex from the DNA binding site, terminating the action of the hormones

8. PLP IN TRANSAMINATION The transfer of an amino group from an amino acid to a keto acid with the formation of a new amino acid and the a new keto acid. Catalysed by a group of enzymes called transaminases(aminotransferases) and pyridoxalphosphate (PLP) as a co-factor Mechanism of transamination STEP 1 Transfer of amino group from Amino acid to the coenzyme PLP to form pyridoxamine phosphate Amino acid1 is converted into keto acid STEP 2 Amino group of pyridoxamine phosphate is the transferred to a keto acid to produce a new amino acid and enzyme with PLP is regenerated.

9. PLP mediated histidine decarboxylation PLP-Mediated Histidine Decarboxylation Proceeds via an Imine Intermediate

10. GYCOGEN PHOSPHORYLASE Catalyzes the rate limiting step in glycogenolysis in animals by releasing glucose-1-phosphate from the terminal alpha-1,4-glycosidic bond. Gycogen phosphorylase has a pyridoxal phosphate at each catalytic site, which links with the basic residues and covalently forms a Schiff base linkage.

11. Biosynthesis of serotonin and melatonin

12. Function of plp PLP also plays a role in conversion of: Levodpa Dopamine Glutamine (Excitatory neurotransmitter) GABA (Inhibitory neurotransmitter ) PLP is involved in various beta elimination reactions Reactions carried out by serine dehydratase and GDP-4-keto-deoxymannose-3-dehydratse Degradation of serine to pyruvate is an example of a PLP catalysed beta elimination reaction

13. a-proton of serine is abstracted by a basic active-site lysine residue (step 1) elimination of water (step 2), the dehydrated substrate is freed from the PLP coenzyme (step 3) by Schiff base transfer tautomerizes to the imine form (step 4 ) hydrolyzed to pyruvate (step 5 )

14. Vitamin B6 deficiency is rare Moderate deficiency results in abnormalities of tryptophan and methionine metabolism. Increased sensitivity to steroid hormone action may be important in the development of hormone dependent cancer of the breast, uterus, and prostate, and vitamin B6 status may affect the prognosis. In excess vitamin B6 causes sensory neuropathy

15. Thiamine pyrophosphate ( tpp )

16. Thiamine pyrophosphate ( tpp ) T hiamine pyrophosphate (TPP/ ThPP ), thiamine diphosphate ( ThDP ) is a thiamine ( Viatmin B1) derivate which is produced by the enzyme thiamine diphosphokinase TPP is a co-factor that is present in all living systems, in which it catalyses several biochemical reactions Conversion of thiamine into coenzyme form (TPP)

17. STRUCTURE OF TPP The part of TPP molecule that is most commonly involved in reactions is the thiazole ring ( "reagent portion" ), which contains  nitrogen  and  sulfur The C2 of this ring is capable of acting as an  acid  by donating its  proton  and forming a  carbanion Normally , reactions that form carbanions are highly unfavorable , but the positive charge on the tetravalent nitrogen just adjacent to the carbanion stabilizes the negative charge, making the reaction more favorable . (A compound with positive and negative charges on adjacent atoms is called an  ylid  or ylide , so sometimes the carbanion form of TPP is referred to as the " ylid form" Pyrimidine   ring Thiazole  ring Pyrophosphate

18. Metabolic pathways requiring Tpp

19. TPP is the coenzyme for the three multi enzyme complexes that catalyse oxidation decarboxylation reactions: Pyruvate dehydrogenase in carbohydrate metabolism α - keto glutarate in citric acid cycle Branched chain keto chain dehydrogenase involved in the metabolism of leucine, isoleucine and valine TPP also plays a role in nerve conduction. It phosphorylates and activates a chloride channel in the nerve conduction

20. TPP in Pyruvate dehydrogenase complex PDH complex is large and highly integrated of three kinds of enzyme : Pyruvate dehydrogenase dihydrolipoyl transacetylase dihydrolipoyl dehydrogenase At least two additional enzymes regulate the activity of complex and five coenzymes: TPP, lipoic acid, CoASH , FAD and NAD+

21. It is a cofactor for the transketolase reactions in the pentose phosphate pathway of the carbohydrate metabolism. Reversible transformation of the pentoses into the glycolytic intermediates (fructose-6-phosphate, glutaraldehyde-3-phosphate) Transketolase transfers the 2carbon unit comprising carbon 1 and 2 of the ketose onto the aldehyde carbon of an aldose sugar. This reaction requires Mg2+ and TPP as cofactors TPP in transketolase reaction

22. Thiamine is also responsible for the metabolism of the tryptophan (as a coenzyme for tryptophan pyrrolase ) T ryptophan oxygenase (tryptophan pyrrolase ) opens the indole ring, incorporates molecular oxygen, and forms N- formyl kynurenine TPP in tryptophan metabolism L- Tryptophan Tryptophan oxygenase N-L- Formylkynurenine

23. Deficiency of thiamine efficiency of enzymes Pyruvate acetyl CoA F low of acetyl CoA through TCA cycle Production of reduced electron carrier NADH and the ATP produced via oxidative phosphorylation Thiamine deficiency and impaired reactions

24. Coenzyme A

25. COASH CoASH , CoA and HSCoA (Coenzyme A) is a coenzyme, notable for its role in the synthesis and oxidation of fatty acids and the oxidation of pyruvate in the citric acid cycle. Discovery of the structure The structure of coenzyme A was identified in the early 1950s at the Lister institute, London, together with the other workers at Harvard medical school and Massachusetts general hospital. β - Mercaptoethylamine Pantothenic acid 3’-Phosphoadenosine diphosphate Ribose 3’-phosphate Adenine

26. Biosynthesis Coenzyme A is synthesised in five step process that requires four molecules of ATP from pantothenate and cysteine. Pantothenate (Vitamin B5): is phosphorylated to 4’-phosphopantothenate by the enzyme pantothenate kinase Cystein is added to 4’-phosphopantothenate by the enzyme phosphopantothenocystien synthetase to form 4’-phospo-N-pantothenoclcystein (PPC) PPC is decarboxylated to 4’-phosphopanthetien by phosphopantothenocysteine decarboxylase 4’- phosphopanthein is adenylated to form dephospho -CoA by the enzyme phosphopantetheine adenylyl transferase Dephospho -CoA is phosphorylated to coenzyme A by the enzyme dephospho coenzyme A kinase.

27. FUNCTIONS Since coenzyme A is, in chemical terms, a  thiol , it can react with carboxylic acids to form thioesters, thus functioning as an acyl group carrier It assists in transferring fatty acids from the  cytoplasm to  mitochondria A molecule of coenzyme A carrying an acetyl group is also referred to as  acetyl-CoA . When it is not attached to an acyl group, it is usually referred to as ' CoASH ' or ' HSCoA ' Coenzyme A is also the source of the  phosphopantetheine   group that is added as a prosthetic group to proteins such as acyl carrier protein  and  formyltetrahydrofolate dehydrogenase

28. Oxidation of Fatty acids ( β -oxidation) Activation of fatty acids Transport of fatty acids from blood to mitochondria Oxidation in mitochondrial matrix Activation of fatty acids Function Fatty acid ATP Acyl adenylate Acyl adenylate CoASH Fatty acyl CoA

29. Oxidation of pyruvate in the TCA cycle The carboxyl group is removed from pyruvate, releasing carbon dioxide NAD+ is reduced to NADH An acetyl group is transferred to coenzyme A, resulting in acetyl CoA Function

30. Thank You