Role of inorganic ions in biochemistry

Biochemistry generally focuses on reactions and interactions of biological and organic molecules.

Interactions with inorganic molecules equally important

Defination-inorganic biochemistry

The branch of biochemistry concerned with the role of inorganic substances in biochemical systems

Various roles of metal ions :

Linking distant residues or parts of the amino acids in the proteins together. Mediating interactions between the protein and a ligands. Positioning themselves in the active sites of the macromolecules as nucleophilic catalysts or as a key component in the electron transfer chain.

metalloproteins

A protein containing a metal ion bound is called metalloproteinMany metalloproteins catalyze important cellular reactions and are thus more specifically called metalloenzymes the metal center can serve as a Lewis acidic site to activate substrates for nucleophilic displacement reactions (that is, hydrolysis).

Proteins fold to form their functional form by bonding with metal ion.

Eg hemoglobin

Coordinate bond

The electronic structure of a coordination complex can be described in terms of the set of ligands each donating a pair of electrons to a metal centre.

Metal ions have a few characteristics that increase chemical activity:

positive charge

ability to form strong bonds that are kinetically favored

and in some cases their ability to be stable in multiple oxidation states.

Example

Carbonic anhydrase was the first known enzyme to contain zinc

Carbonic anhydrase carries out interconversion of carbondioxide and water to bicarbonate and proton.

The reaction catalyzed by carbonic anhydrase is:

Metal-activated enzymes absolute requirement for the metal ion

Phosphofructokinase is an example of a metal- activated enzyme, which catalyzes the reaction

fructose-6-phosphate + ATP → fructose-1,6-

bisphosphate + ADP

A divalent metal ion (Mg 2+ ) is needed to coordinate the phosphate groups on the ATP molecule in order for phosphofructokinase to successfully catalyze this reaction

metal ions are normally incorporated into the enzymes during enzyme synthesis For example, horse liver alcohol dehydrogenase contains two tightly bound zinc ions . The first zinc ion is structural: bound to four cysteine side chains essential to maintain the structural integrity The second zinc ion is catalytic: bound to the side chains belonging to two cysteines and one histidine at the active site of the enzyme, participates in the catalytic cycle of the enzyme.