Thiamin is a co-enzyme for
Ans. a (Transketolase) (Ref. Harper's Biochemistry-27th ed. 498).# Transketolase is a thiamine-requiring enzyme involved in the HMP shunt.# Other enzymes requiring Thiamine are n Pyruvate dehydrogenase & n a - ketoglutarate dehydrogenase.# Transketolase transfers the two-carbon unit comprising carbons 1 and 2 of a ketose onto the aldehyde carbon of an aldose sugar. It therefore effects the conversion of a ketose sugar into an aldose with two carbons less and simultaneously converts an aldose sugar into a ketose with two carbons more.# The reaction requires Mg2+ and thiamine diphosphate (vitamin B,) as coenzyme.# Measurement of erythrocyte transketolase and its activation by thiamine diphosphate is used to assess thiamine nutritional status.0# Transaldolase allows the transfer of a three-carbon dihydroxyacetone moiety (carbons 1-3) from the ketose sedohep- tulose 7-phosphate onto the aldose glyceraldehyde 3-phosphate to form the ketose fructose 6-phosphate and the four-carbon aldose erythrose 4-phosphate.VitaminFunctionsDeficiency diseaseARetinol, b-caroteneVisual pigments in the retina; regulation of gene expression and cell differentiation; b-carotene is an antioxidantNight blindness, xerophthalmia; keratinization of skinDCalciferolMaintenance of calcium balance; enhances intestinal absorption of Ca2+ and mobilizes bone mineralRickets = poor minertialization of bone; osteomalacia = bone de-mineraizationETocopherols, tocotrienolsAntioxidant, especially in cell membranesExtremely rare - serious neurologic dysfunctionKPhylloquinone, menaquinonesCoenzyme in formation of g-carboxyglutamate in enzymes of blood clotting and bone matrix diseaseImpaired blood clotting, hemorrhagic diseaseB1ThiaminCoenzyme in pyruvate and a-ketoglutarate, dehydrogenases, and transketolase; poorly defined function in nerve conductionPeripheral nerve damage (beriberi) or central nervous system lesions (Wernicke-Korsakoff syndrome)B2RiboflavinCoenzyme in oxidation and reduction reactions; prosthetic group of flavoproteinsLeisons of corner of mouth, lips, and tongue; seborrheic dermatitis Niacin, Nicotinic acid, nicotinamideCoenzyme in oxidation and reduction reaction, functional part of NAD and NADPPellagra-photosensitive dermatitis, depressive psychosisB6Pyridoxine, pyridoxal, PyridoxamineCoenzyme in transamination and decarboxylation of amino acids and glycogen phosphorylase; role in steroid hormone actionDisorders of amino acids metabolism, convulsions Folic acidCoenzyme in transfer of one-carbon fragmentsMegaloblastic anemiaB12 CobalaminCoenzyme in transfer of one-carbon fragments and metabolism of folic acidPernicious anemia = megaloblastic anemia with degeneration of the spinal cordPantothenic acidFunctional part of CoA and acyl carrier protein, fatty acid synthesis and metabolism HBiotinCoenzyme in carboxylation reactions in gluconeogenesis and fatty acids synthesisImpaired and carbohydrate metabolism, dermatitisCAscorbic acidCoenzyme in hydroxylation of proline and lysine in collagen synthesis; antioxidant; enhances absorption of ironScurvy - impaired wound healingLoss of dental cement, subcutaneous hemorrhagePentose phosphate pathway (HMP shunt).Produces NADPH, which is required for fatty acid and steroid biosynthesis and for glutathione reduction insideRBCs. All reactions of this pathway occur in the cytoplasm. No ATP is used or produced. Sites- lactating mammary glands, liver, adrenal cortex (sites of fatty acid or steroid synthesis), and RBCs.ReactionsKey enzymesProductsOxidative (irreversible)Glucose-6-phosphate dehydrogenaseNADPH (for fatty acid and steroid synthesis, glutathione reduction, and cytochrome P-450).Nonoxidative (reversible)Transketolases (require thiamine)Ribose-5-phosphate (for nucleotide synthesis), G3P, F6P (glycolytic intermediates)
Transketolase
Alanine transferase
ALA synthase
Cystathionine synthase
Vitamins and Minerals