Sinh học - Chapter 7 (part 2): Cofactors

Chapter 7 (part 2)CofactorsBiotinWater soluble VitaminProduced by gut microflora which supplies ½ RDADeficiencies are rareConsuming 6 raw eggs a day can cause deficiencies due to the presence avidin (biotin binding protein). Biotin cofactorInvolved in ATP dependent carboxylation rxnsCovalently bound to enzyme through amide linkage w/lysineImpt. Biotin enzymes = acetyl-CoA carboxylase, pyruvate carboxylase FolateWater soluble vitaminFolate impt. during pregnancy to prevent neural tube defects in fetus (I.e. spina bifida)Vitamin B12 deficiencies cause folate deficienciesHas a poly-glutamate tail formed by gamma-carboxy and alpha amino groups (unusual peptide bond).pterinPABAglutamateTetrahydrofolate (THF)Folate is converted to THF by the addition of 4 hydrogens to the pterin ring.Impt. in transfer of one-carbon unitsPterin ring impt. functional groupCan transfer one carbon units at the oxidation level of methanol, formaldehyde, or formic acid.Cobalamin (B12)Water soluble VitaminCorrin ring with Cobalt cation Involved in intramolecular rearrangements, methyl group transfer, reduction of ribonucleotides to deoxyribonucleotides.Forms radical species Pantothenic acid/Coenzyme A (CoA)Pantothenic acid is water soluble vitaminCo-enzyme A involved in acyl group transferSulfhydroyl group impt. Hydrophobic acyl groups (fatty acids) are made more water soluble w/CoA attachedLipoic acid/LipoamideNot a vitaminImportant reactive groups are the sulfur atomsDisulfide can be reduced to form 2 sulfhydryl groupsInvolved in acyl group transfer reactionsCo-factor covalently attached to enzyme through amide linkage with lysine residueLipoamideFat soluble VitaminsVitamin 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 bonesVitamin E – antioxidantreduced formoxidized formVitamin 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 surfaceOnly fat soluble cofactor that functions as a cofactorDrugs inhibit reduction of oxidized form of vitamin KUbiquinone/PlastoquinoneLipid soluble electron carriers.Impt in electron transport chainsCan accept or donate electrons one or two at a timeProtein coenzymesUsually small proteinsActive groups are either prosthetic groups or part of protein backboneParticipate in group transfer and oxidation/reduction rxnsacyl carrier proteinbiotin carboxyl carrier proteincytochromesProtein coenzymeHeme containing proteinsFe3+ can undergo reversible one electron reductionImpt in redox rxnsClassified based on the basis of their visible absorbance spectra