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Chapter 7 (part 2)

Chapter 7 (part 2). Cofactors. Biotin. Water soluble Vitamin Produced by gut microflora which supplies ½ RDA Deficiencies are rare Consuming 6 raw eggs a day can cause deficiencies due to the presence avidin (biotin binding protein). Biotin cofactor.

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Chapter 7 (part 2)

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  1. Chapter 7 (part 2) Cofactors

  2. Biotin • Water soluble Vitamin • Produced by gut microflora which supplies ½ RDA • Deficiencies are rare • Consuming 6 raw eggs a day can cause deficiencies due to the presence avidin (biotin binding protein).

  3. Biotin cofactor • Involved in ATP dependent carboxylation rxns • Covalently bound to enzyme through amide linkage w/lysine • Impt. Biotin enzymes = acetyl-CoA carboxylase, pyruvate carboxylase

  4. glutamate PABA pterin Folate • Water soluble vitamin • Folate impt. during pregnancy to prevent neural tube defects in fetus (I.e. spina bifida) • Vitamin B12 deficiencies cause folate deficiencies • Has a poly-glutamate tail formed by gamma-carboxy and alpha amino groups (unusual peptide bond).

  5. Tetrahydrofolate (THF) • Folate is converted to THF by the addition of 4 hydrogens to the pterin ring. • Impt. in transfer of one-carbon units • Pterin ring impt. functional group

  6. Can transfer one carbon units at the oxidation level of methanol, formaldehyde, or formic acid.

  7. Cobalamin (B12) • Water soluble Vitamin • Corrin ring with Cobalt cation • Involved in intramolecular rearrangements, methyl group transfer, reduction of ribonucleotides to deoxyribonucleotides. • Forms radical species

  8. Pantothenic acid/Coenzyme A (CoA) • Pantothenic acid is water soluble vitamin • Co-enzyme A involved in acyl group transfer • Sulfhydroyl group impt. • Hydrophobic acyl groups (fatty acids) are made more water soluble w/CoA attached

  9. Lipoic acid/Lipoamide • Not a vitamin • Important reactive groups are the sulfur atoms • Disulfide can be reduced to form 2 sulfhydryl groups • Involved in acyl group transfer reactions • Co-factor covalently attached to enzyme through amide linkage with lysine residue

  10. Lipoamide

  11. Fat soluble Vitamins • Vitamin A (retinol) derived from b-carotene impt for vision, regulation of gene expression during cell differentiation, teratogenic • Vitamin D – impt in Ca absorption, regulates intestinal absorption and deposition in bones • Vitamin E – antioxidant

  12. Vitamin K is a cofactor for the enzyme that carboxylates certain glutamate residues on prothrombin to g-carboxyglutamate residues. Ca+ binds g-carboxyglutamate residues causes protein to adhere to platelet surface Only fat soluble cofactor that functions as a cofactor Drugs inhibit reduction of oxidized form of vitamin K reduced form oxidized form

  13. Ubiquinone/Plastoquinone • Lipid soluble electron carriers. • Impt in electron transport chains • Can accept or donate electrons one or two at a time

  14. Protein coenzymes • Usually small proteins • Active groups are either prosthetic groups or part of protein backbone • Participate in group transfer and oxidation/reduction rxns • acyl carrier protein • biotin carboxyl carrier protein

  15. cytochromes • Protein coenzyme • Heme containing proteins • Fe3+ can undergo reversible one electron reduction • Impt in redox rxns • Classified based on the basis of their visible absorbance spectra

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