1st year MBBS- (Continuation from last class)

1.Write short note on: a) Coenzyme b) Cofactor c) Isoenzyme(Isozyme)

Answer:

Coenzyme

A coenzyme is a substance that works with an enzyme to initiate or aid the function of the enzyme. It can be considered a helper molecule for a biochemical reaction. Coenzymes are small, nonproteinaceous molecules that provide a transfer site for a functioning enzyme. They are intermediate carriers of an atom or group of atoms, allowing a reaction to occur. Coenzymes are nonprotein organic molecules that bind loosely to an enzyme. Many (not all) are vitamins or are derived from vitamins. Many coenzymes contain adenosine monophosphate (AMP). Coenzymes maybe described as either cosubstrates or prosthetic groups.

Cofactors are inorganic species or at least nonprotein compounds that aid enzyme function by increasing the rate of catalysis. Typically, cofactors are metal ions. Some metallic elements have no nutritional value, but several trace elements function as cofactors in biochemical reactions, including iron, copper, zinc, magnesium, cobalt, and molybdenum. Some trace elements that appear to be important for nutrition do not appear to act as cofactors, including chromium, iodine, and calcium.

Isoenzymes

Multiple enzyme forms of one enzyme are known as isoenzymes (or isozymes). Isoenzymes of one enzyme group are often expressed to differing extents in different tissues.

Lactate dehydrogenase (LDH) is a tetrameric enzyme composed of all possible arrangements of two different protein subunits: the subunits are known as H (for the heart) and M (for skeletal muscle).These subunits come together in various combinations, leading to five distinct isoforms. The all H isoform is characteristic of that from heart tissue and the all M isoform is typically found in skeletal muscle and liver.