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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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biotin
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
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
folate

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).
tetrahydrofolate thf
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
slide6

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

cobalamin b12
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
pantothenic acid coenzyme a coa
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
lipoic acid lipoamide
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
fat soluble vitamins
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
slide12

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

ubiquinone plastoquinone
Ubiquinone/Plastoquinone
  • Lipid soluble electron carriers.
  • Impt in electron transport chains
  • Can accept or donate electrons one or two at a time
protein coenzymes
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
cytochromes
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