Enzymes are bio-catalysts or organic catalysts present in living cells. They regulate various biochemical reactions without themselves being utilized in those reactions.
They enhance a reaction due their presence in the body.
They are involved in many physiological processes starting from digestion, excretion and even to reproduction.
Without enzymes body physiology slows down and may lead to dysfunction.
There are many fatal disorders linked to enzyme deficiency.
Enzymes are present either in whole body or confined few places in the body. They are present inside the cell and cell organelles. While some of them are secreted from exocrine glands for local action.
The enzymes can be differentiated into many types based on their physiological location, chemistry and also mode of action.
Types of enzymes based on physiological location.
Systemic enzymes: These are the set of enzymes present in whole body. They are mostly present inside the individual cells or their organelles. They are produced in all the body cells and confined for specific action. They cannot be given as substitutes in case of disorders arising out of their deficiency. Ex: cyclo-oxygenases.
Local enzymes: These are the enzymes which produce their effect only at certain parts of the body. Like hormones they are formed inside some specific glands and then secreted near by for physiological action. Ex: Digestive enzymes. But unlike systemic enzymes, they can be substituted externally in case of deficiency. Ex: Digestive enzymes.
In case of deficiency, similar digestive enzymes obtained from other sources can be administered for therapeutic effect.
Ex: Papain is isolated from papaya fruit by enzyme immobilization technique and used to enhance digestion.
Types of Enzymes based on chemistry:
These are of two types as
1. Simple enzymes
2. Complex enzymes
Simple enzymes are those which are made of only a protein part and nothing else.
Ex: digestive enzymes like amylase, pepsin etc.
Complex enzymes are those which have a protein part and also a non-protein part. The non-protein part plays a key role in the action of enzyme besides protein. The protein part is called apo-enzyme and the non-protein part is prosthetic group. The prosthetic group can be an inorganic part like Zn, Cu etc. which is called as co-factor. The prosthetic group that contains organic group (ex: vitamin B3 etc.) are called as co-enzyme.
But the modern classification is based on International Union of Biochemists.
Types of enzymes based on IUB:
Enzymes are briefly classified based on the reaction they are involved.
1) Oxido-reducatases: They catalyse oxidation reduction reactions. Here is there is either addition of hydrogen (reduction) or removal of oxygen (oxidation). Also it can be addition of oxygen moiety (oxidation) or removal of oxygen moiety (reduction).
Ex: alcohol dehydrogenase catalyses the following reaction.
Acetaldehyde+ NADH2—————->Ethyl alcohol + NAD.
2) Hydrolases: They bring about hydrolysis of substances by addition of water. i.e. they bring about breakdown by addition of water molecule.
Glucose-6-phosphate+H2O ———–> Glucose + phosphoric acid.
These are of specific types like
2.a) Carbohydrases: These enzymes hydrolyze carbohydrates.
Sucrose———-sucrase——–> Glucose + fructose.
2.b) Esterases: These enzymes hydrolyze lipids.
oil/ fats—————–lipase——-> glycerol+ fatty acids.
2.c) Proteases: These are the enzymes that hydrolyze proteins.
3) Ligases: These enzymes catalyse formation of bonds. They are also called as synthetases.
Ex: Acetyl CoA (vit-B5)
ATP+ acetic acid+ CoA——————>AMP+P-Acetyl CoA
4) Lyases: These enzymes bring about lysis (breakage) of double bonds. They remove groups from double bonds.
Pyruvic acid ——————–> Actaldehyde + CO2.
5) Transferases: These enyzmes help in transfer of groups.
Ex: Glucose+ ATP—glucokinase—–>Glucose-6-phosphate+ADP.
6) Isomerase: Iso-“similar”, mers-“pieces”. As the name indicates they catalyse isomerisation.
Glucose-6-phosphate ————–>Fructose-6-phosphate. In presence of phosphoglucoisomerases.