cofactors

Examples of cofactors in the following topics:

• Cofactors and Energy Transitions

  • Cofactors are either organic or inorganic.
  • An inactive enzyme without the cofactor is called an apoenzyme, while the complete enzyme with cofactor is the holoenzyme.
  • Some enzymes or enzyme complexes require several cofactors.
  • Organic cofactors are often vitamins or are made from vitamins.
  • Cofactors can be divided into two broad groups: organic cofactors, such as flavin or heme, and inorganic cofactors, such as the metal ions Mg2+, Cu+, Mn2+, or iron-sulfur clusters.

• Cofactors, Minors, and Further Determinants

  • The cofactor of an entry $(i,j)$ of a matrix $A$ is the signed minor of that matrix.
  • Specifically the cofactor of the $(i,j)$ entry of a matrix, also known as the $(i,j)$ cofactor of that matrix, is the signed minor of that entry.
  • The cofactor of $a_{ij}$ entry of a matrix is defined as:
  • Note: If $i+j$ is an even number, the cofactor coincides with its minor: $C_{ij}=M_{ij}$.
  • Explain how to use minor and cofactor matrices to calculate determinants

• Phenylketonuria (PKU)

  • A rarer form of hyperphenylalaninemia occurs when PAH is normal, but there is a defect in the biosynthesis or recycling of the cofactor tetrahydrobiopterin (BH4) by the patient.
  • This cofactor is necessary for proper activity of the enzyme.
  • Dihydrobiopterin reductase activity is to replenish quinonoid-dihydrobiopterin back into its tetrahydrobiopterin form, which is an important cofactor in many metabolic reactions in amino acid metabolism.
  • Those with this deficiency may produce sufficient levels of PAH, but since tetrahydrobiopterin is a cofactor for PAH activity, deficient dihydrobiopterin reductase renders any PAH enzyme non-functional.
  • Tetrahydrobiopterin is also a cofactor in the production of L-DOPA from tyrosine and 5-hydroxy-l-tryptophan from tryptophan, which must also be supplemented as treatment in addition to the supplements for classical PKU.

• Control of Metabolism Through Enzyme Regulation

  • Many enzymes only work if bound to non-protein helper molecules called cofactors and coenzymes.
  • Cofactors are inorganic ions such as iron (Fe2+) and magnesium (Mg2+).
  • Pyruvate dehydrogenase is a complex of several enzymes that requires one cofactor and five different organic coenzymes to catalyze its chemical reaction.
  • The availability of various cofactors and coenzymes regulates enzyme function.

• Role of Vitamin K

  • Coagulation is a complex cascade that requires many different cofactors and molecules to occur.
  • Vitamin K, calcium, and phospholipids are necessary cofactors for proper coagulation, and people deficient in these substances will be more susceptible to uncontrolled bleeding.
  • Calcium and phospholipids (a platelet membrane constituent) are required cofactors for prothrombin activation enzyme complexes to function.

• Nanoarchaeum and Aciduliprofundum

  • N. equitans genome consists of a single circular chromosome, and lacks almost all genes required for synthesis of amino acids, nucleotides, cofactors, and lipids, but encodes everything needed for repair and replication. 95% of its DNA encodes for proteins for stable RNA molecules.
  • Nanoarchaeum cannot synthesize most nucleotides, amino acids, lipids, and cofactors.

• Biomolecules

  • Metalloprotein is a generic term for a protein that contains a metal ion cofactor.
  • In addition to donor groups that are provided by amino acid residues, a large number of organic cofactors function as ligands.

• Enzyme Catalysis

  • Covalent catalysis: covalent bonding to side chains or cofactors can lower the energy of the transition state.

• Iron-Binding Proteins

  • They are carrier proteins (those used to move ions and molecules across membranes) and more generally metalloproteins (those which contain a metal ion cofactor).

• Gene Inversion

  • For this to occur, there is typically one or more cofactors (to name a few: DNA-binding proteins and the presence or absence of DNA binding sites) and a site specific recombinase.