Specificity Property

Only a few enzymes exhibit absolute specificity property when they catalyze for only one particular reason ( a particular fixed reaction). Other enzymes will be specific for a particular type of chemical bond or functional group. The property of enzymes describes how restrictive the enzymes are in their choice of any substrate ( a completely specific enzyme that consists of only one substrate). 

The specificity property of serine proteases is usually not that high because they have very similar active sites which act through the same proteolytic mechanism. However, single serine protease can act on various substrates, although at consecutively different rates. The substrate fitting in the active site of the particular enzyme is of crucial importance to the outcome of the reaction caused by the enzyme-substrate reaction. 

The property of the substrate that indicates the degree to which the substrate is attached to and cleaved by different enzymes is what we call selectivity. The specificity property of enzymes are divided into six groups :

Bond Specificity

By specificity property, we can define bond specificity as relative specificity (characteristics whereby in biochemical procedure which contains a molecule that interacts with its numerous substrates). 

Bond specificity or relative specificity is defined as the enzymes showing these two types of specificity specific to particular substrates that share similar bonds and structures. This specification meant that only certain types of bonds, such as peptide bonds, glycosidic bonds, and ester bonds, are specific to only these types of bonds.

For example, the alpha-amylase enzyme can hydrolyze an alpha-1-4 glycosidic linkage in both glycogens and starch. Similarly, ester bonds can be hydrolyzed by lipase ( ester bonds are formed due to the bond between glycerol and fatty acids).

Group Specificity

Group specificity is also called moderate specificity. In group specificity, an enzyme is particularly specific to a bond and also specific to the groups surrounding the bond. The specificity power in group specificity is much more than that of specificity power in bond specificity.  

Two general classes of proteinases (Endopeptidases and exopeptidases are two classic examples of group specificity. Group specificity derives that an enzyme will start getting catalyzed at a reaction on a function group of several molecules (for example, cleaving an alcohol group or working only on aldohexose sugars). 

Peptides are hydrolyzed by pepsin, where amino groups are from aromatic amino acids-phenylalanine, tyrosine, and tryptophan which catalyze the same reaction for obtaining similar substrates. Their action is group-specific, for example, a methyl group and a phosphate group. Hexokinases transfer phosphates to hexoses. One vital exam of group specificity is pepsin; pepsin is an enzyme used in digestion produced by chief cells in the stomach. 

Substrate Specificity

Substrate specificity also possesses another name known as absolute specificity. However, in the case of Substrate specificity or absolute specificity, the concentration of specificity is much higher. Only to one particular substrate and only to one reaction, the enzymes that show substrate specificity are only specific to these particular conditions.

In specificity as a property of an enzyme, substrate specificity or absolute specificity is usually thought of as being exclusive, which means one enzyme at a time acts upon only one specific substrate. The procedure of Substrate specificity or absolute specificity only catalyzes when its enzyme will catalyze one reaction with its specific substrate.

For example, an enzyme specific for the degradation of lactose (lactase) into two parts sugar monosaccharides, glucose, and galactose. Glucokinase, another example of Substrate specificity or absolute specificity, is where the enzymes are involved in the phosphorylation of glucose to its glucose-6-phosphate. It is mainly carried out in the liver, and also it is the main isozyme of Hexokinase. Its absolute specificity refers to the glucose being the only hexose capable of being its substrate, as opposed to Hexokinase, which accommodates many hexoses as its substrate.

Optical Specificity

The enzyme of optical specificity is also known as stereospecificity. Here in optical specificity, the enzyme is not only specific to the substrate but also its particular optical configuration. The optical specificity enzyme is often considered the specificity property possessing more or less the highest specificity seen by any class of enzyme present in the living world. 

Geometric Specificity

Also, in geometric specificity, a particular single enzyme usually acts on various substrates that share similar molecular geometry, and here their specificity is comparatively much less. Also, the specificity case is very low in geometric specificity.

For example, we can take Alcohol dehydrogenase, which can oxidize both ethanol and methanol to make the corresponding aldehydes (as both these Alcohols mentioned above share similar molecular geometry).

Cofactor Specificity

The non-protein part of the enzymes is what we call cofactors. The cofactors are required to carry out the functioning of some particular enzymes. The enzymes need cofactor specificity for their activities. Applying the correct combination of substrate and cofactor allows the enzymatic reaction process. When these specific cofactors are not present during the process, the enzyme will be inactive even if there are no absences or plenty of Substrates.

For example, The cofactor specificity of nicotinamide enzymes plays an important role in maintaining and regulating the metabolic processes and accomplishing cellular homeostasis. Various studies of specificity have used tools for enzyme engineering or a directed evolution approach to change and switch the cofactor preference of specific oxidoreductases.

Conclusion

Since the substrate needs to fit into the active site of the enzyme before the whole process of catalysation can start, only the proper and well-designed molecules can serve as substrates for the need of a specific enzyme. Also, in many cases, an enzyme will react with only one particular naturally occurring molecule. 

When the specificity of enzymes was first studied, it was concluded that” they are bound to react with only one compound at a time. But in most cases, usually, a molecule other than the natural substrate present is allowed to be synthesized in the laboratory. Hence it is enough like the natural substrate when it reacts with the enzyme.