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Definition of enzyme and enzyme catalysis

Enzyme is a protein that fasten up the rate of chemical reaction within a living organism. An enzyme acts as catalyst where catalyst is defined as substance that increase the rate of chemical reaction by lowering the activation energy by providing the alternative path. Enzyme catalyst will not be consumed or permanently altered themselves during the chemical reaction. Thus, enzyme catalysis is a process that use an enzyme as catalyst in the chemical reaction. Chemical reaction is the process of converting one or more specific substance (reactant, substrate or reagent) into another type of specific substance (product). As a catalyst, an enzyme can be use in the same chemical reaction over and over again.

Enzyme specificity

Enzyme specificity is defined as the ability of an enzyme to bind with specific substrate or catalyze in a specific set of chemical reaction. Specificity of an enzyme is one of the properties that make enzyme so important as identification and research tools. Enzymes exhibit relative to the reaction they catalyze. A few enzymes possess absolute specificity such as they will catalyze only one particular reaction. Other enzymes will be specific for a particular type of chemical bond or functional group. There are six types of enzyme specificity which are absolute specificity, linkage specificity, group specificity and stereochemical specificity, geometrical specificity and lastly is co-factor specificity.

?Absolute specificity
Also known as substrate specificity.The enzyme will catalyze only one reaction which means that an enzyme acts on one specific substrate.
?Lactase is an enzyme specific for the breakdown of lactose into two sugar monosachharides, glucose and galactose.
?Maltase enzyme can only act on the ?-1-4-glycosicidic linkage of two glucose molecules in maltose.
C12H22O11 (aq) + H2O(l) ? 2C6H12O6 (aq)

?Linkage specificity
Also known as bond specificity.They enzyme will act on particular on a particular type of chemical bond no matter of the rest of the molecular structure.
An enzyme cleave specific linkage of the reactant in order to create two products linked together. As example, ester linkage is formed between glycerol and any fatty acid when lipase is being hydrolyzed. Other than that, proteinases can hydrolyze peptide bonds formed by amino acid in the protein.
?Group specificity
The enzyme will act only on molecules that have specific functional groups, such as amino (aromatic structures), phosphate groups, and methyl groups.
?Pepsin which act as an enzyme that vital in digestion of food ingested in our diet, that will hydrolyzes or broken down the peptide bonds by adding water in between hydrophobic amino acids with recognition for aromatic side chains such as phenylalanine, tryptophan, and tyrosine.
?Chymotrypsin wich is a digestive enzyme at pancreatic juice which can hydrolyze a peptide bond in which carboxyl group is contributed by any aromatic amino acid such as phenlyalanine, tyrosine and tryptophan.
?Trypsin, a serine protease digestive system which can hydrolyze a peptide bond in which amino group is contributed by any basic amino acid such as lysine, arginine and histidine.
?Streochemical specificity
The enzyme will act on a particular steric or optical isomer. Stereochemical molecules differ in the way in which they rotate plane polarized light, or orientations of linkage. Enzymes that are stereochemically specific will bind substrates with these particular properties. Streochemical enzyme is considered as the highest specificity shown by any class of enzyme in the living world.
?L-amino acid oxidase acts only on L-amino acids. Same goes to D-amino acids oxidase acts only on D-amino acids.??-glycosides will only react with ?-glycosidic bonds which are present in cellulose, but absent in starch and glycogen which contain ?-glycosidic linkages. This is relevant in how mammals are able to digest food. For instance, the enzyme amylase is present in mammal saliva, that is stereo-specific for alpha linkages, this is why mammals are able to efficiently use starch and glycogen as form of energy, but not cellulose ( because it is a beta-linkage).Only single enzyme can act on different substrate having similar molecular geometry and hence the specificity is very less.
?Since both ethanol and methanol have same molecular geometry, alcohol dehydrogenase can oxidize both methanol and ethanol to produce aldehydes. ?Co-factor specificity
Co-factors are known as non-protein part of the enzyme which required to activate some enzyme. Enzyme which need co-factors for the their enzymatic activity possess co-factor specificity. Only the right combination of substrate and co-factor allow enzymatic reaction. Without specific co-factor, they enzyme will be inactive.

Mechanism for enzymatic reaction

As for the mechanism, there are different theorist comes out by expert to explain on how the enzyme action:

(i)Lock and key theory:

According to Fildes only a particular substrate could be mix with the active site of a certain enzyme as a specialized key fits to open a specific lock. In this enzyme molecule produce an active site to fit in with the substrate forming Energy Substrate complex. When reaction completed energy substrate complex breaks into products and enzymes. Enzymes remain unbroken.

(ii)Inducted fit Theory:

According to Koshland, when a one fit substrate comes to bind with the active site of an enzyme, the substrate take into the process, some conformational form of enzyme changes in due to the attractive groups and supporting groups form a complementary structure so that the catalytic group of the active site is in position of the bonds to be broken.

Most of chemical reactions, energy limit that exists has got to get control of the reaction to happen. This barrier are made to avoid complex molecules such as nucleic acids and proteins from automatically decrease, which is important for life maintenance. Metabolic changes are required in a cell, even so some of these complex molecules must be broken down, and this energy limit should be overcome. Heat could provide the additional energy but if too much temperature increase, the cell could be kill. Another ways is adding some catalyst to lower the activation energy level. So, in order for a reaction to occur, reactant molecules must contain enough energy to pass through a potential energy barrier which called as the “activation energy”. All molecules occupy inconstant amounts of energy depending on their recent collision that just happen but, usually, only a few of the molecule have sufficient energy for reaction. The lower the potential energy barrier to reaction, then the reactants have sufficient energy and, hence the faster reaction will occur.

This is where the enzyme play the important role. They react with the substrate to form an intermediate complex or called as transition state that requires minimum energy for the reaction to proceed. The unsteady intermediate compound then breaks down to produce reaction products, and the stable enzyme is free to react with other substrate molecules. For the uncatalysed reaction, it can be found within all catalysts together with enzymes which function by forming a transition state with the reactants of a lower free energy. Even most of the reaction in this potential energy barrier could produce high values in the rate of reaction. On the enzyme, not all part of it are the active site but only certain of it do have which then will bind to substrate. The active site have a spot or hole formed by the bend pattern of the protein. The 3D structure with the chemical and electrical characteristic of a co-factors within the active site, allows only a specific substrate to bind to the site which then determining the enzyme’s specificity.

The end product of reaction depends on the successful completion of each reaction from 5 stage depend on the substrate, each resolve by a specific enzyme. The enzymes in a series can be located closed by each other so it can lower the time taken for reaction process. Beside that intermediate products will continue the process without makes a mess in the pathway, making the process more efficient. By removing intermediates or deduct end products from the reactive pathway, the equilibrium effects are minimized. Since equilibrium is not achieved the reactions will proceed to the right direction.

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