In 1926 James Sumner of Coernell University managed to isolate the enzyme urease from bean extract and then crystalin. In crystalline urease Sumner found a protein. Then John Northrop in 1930 crystalin trypsin and pepsin, John also found that the second enzyme is a protein.
Therefore, the enzyme is a protein that has a specific three-dimensional structure capable of reaction catalyst - a biological reaction. With the enzyme reaction rate will increase but the activation energy is lower than usual reaction. Catalytic activity is influenced by the structure or conformation of the protein. If the protein conformation changes are extreme enzymes such as changing the pH of the concrete, heating and cutting polipeptidanya chain, the catalytic activity will decrease or disappear altogether.
In the cell there are hundreds of different enzymes - different, meaning that the enzyme is only as catalysts for specific reactions. Enzymes can catalysts one group of substrates, those that can catalysts one substrate only, but there also are stereospesifik.Some enzymes only consist of polypeptide chains and contain no other chemical components. Examples of pancreatic ribonuclease enzymes which only consist of polypeptide chains only. But there is also an enzyme that requires additional chemical components are not proteins for catalytic activity. The chemical components are not proteins called cofactors.
Cofactor may be a molecule in the form of inorganic ions - or metal ions may also be an organic molecule. Kofactor form of organic molecules is called a coenzyme. In general coenzyme is derived from water-soluble vitamins such as vitamin B and C.Overall enzyme called holoenzim, part of the enzyme protein called apoenzim and non-protein part called a cofactor. In the process of heating the protein will be damaged (denatured), but the non-protein remains stable.
Apoenzim is a polypeptide chain that has a tertiary structure or kuartenar with the order and composition of certain amino acid residues. Cluster - group or atom of the polypeptide chain enzymes directly involved in catalytic processes, both breaking and bond formation is called the active side. While part of enzymes that play a role in substrate binding referred to as the active center of enzyme.
Enzyme nomenclature is generally given the suffix-ase to the substrate or the types of reactions that cataliyts, such as the protease is an enzyme that catalysts protein hydrolysis reaction. But there is also an enzyme that is named does not explain the substrate or the types of reactions that catalysts, such as the enzyme pepsin, trypsin, and papain.
Committee enzyme biochemistry and biomolecular association international (International Union Biochemistry and Biomolecular Biology / IUBMB) grouping enzyme based reaction, namely:
1. Oxidoreductase is the enzyme that catalysts oxidation reduction reaction.
2. Transferase is a group of enzymes that
catalysts
3. Hidrolase are a group of enzymes that
catalysts
4. Liase are a group of enzymes that
catalysts e
5. Isomerase is an enzyme that catalysts group conversion reaction in molecular structure to form an isomer.
6. Ligase is an enzyme group catalysts ligsi reaction the incorporation of two substrates.
The conversion of reactants into products of enzymatic reactions can be grouped into two steps: first - the first enzyme bound to the substrate to form an enzyme substrate complex are unstable. Then the enzyme-substrate complex is converted further into a product in a second step. In the second step is an interaction between the specific enzyme that is specific amino acids remaining from the enzyme with substrate.
Mechanism of action of each - each enzyme is very specific in accordance with the constituent amino acid residues of the active side of the enzyme in question. In general, these mechanisms can be grouped into four steps as follows:
1. interactions between amino acid residues of enzyme active site, forming clusters that are nucleophiles,
2. formation of a covalent intermediate between substrate with a specific enzyme,
3. acid-base reaction occurs (a shift of electrons) in the enzyme-substrate complex molecules,
4. formation along with the release of the product and return the original enzyme.
To explain the molecular mechanism of enzymatic reactions, there are two general hypotheses that are often used, namely the hypothesis lock and key and induced-fit hypothesis.
a. Lock and key hypothesis
Assumptions used in this hypothesis are:
1. enzyme structure is rigid,
2. during the reaction, no change of enzyme conformation,
3. reactions can take place whenever there is match between the shape of space substrate with the enzyme active center.
According to this hypothesis for an enzymatic reaction can take place then the substrate must have a room that according to the enzyme active center, which is described as the key to the lock.When the appropriate form of space there will be a bond to form a transition complex (enzyme-substrate). Compounds of transition is unstable and will decompose by itself produce the product.
b. Induced-fit hypothesis
The reaction between the substrate with the enzyme take place due to the induction of the substrate molecule. Assumptions used in this hypothesis are:
1. enzyme active center structure is not complementary to the substrate,
2. substrate structure is not rigid,
3. enzyme structure is not rigid.
According to this hypothesis first - first an interaction between the substrate with the enzyme surface in such a manner, resulting in changes in conformation (structure) in the enzyme active center.After the change of conformation at the active center of the enzyme substrate can be bound to the enzyme to form enzyme-substrate complex. In the next step of enzyme-substrate complex decomposes to produce the product and the enzyme is released again as the original enzyme.
Work enzyme can be influenced by several factors, enzyme concentration, substrate concentration, temperature, pH and influence of inhibitors.
a. Enzyme concentration
The speed of a reaction using an enzyme depends on the concentration of enzyme. At a certain substrate concentration, reaction speed increases with increasing concentration of enzyme.
b. Substrate concentration
Experiments showed that with a fixed enzyme concentration, then increase the concentration of substrate will increase the reaction rate. But at a certain concentration limit, there will be no increase in substrate concentration, although the reaction rate is enlarged.
c. Temperature
Therefore, the chemical reaction that can be influenced by temperature, the reaction using an enzyme catalyst can also be affected by temperature. At low temperature chemical reactions take place slowly, whereas at higher temperatures the reaction is faster. However, because the enzyme is a protein, then the temperature rise will cause denaturation process. And if there is the process of denaturation of the enzyme active part will be disrupted. Thus the effective concentration of enzyme is reduced and the reaction velocity will decrease.
d. Effect of pH
Environmental pH changes would affect the effectiveness of the enzyme active part in forming the enzyme substrate complex. In particular pH or pH optimum of an enzyme will work well and cause the highest reaction rate. Therefore, each - each enzyme has different optimum pH.
e. Effect of Inhibitors
Merger substrate with the active enzyme may experience obstacles. Molecules or ions which may inhibit the incorporation reaction is called inhibitors. Barriers that can be done by the inhibitor is not reversible barriers or obstacles reversible. Barriers are not reversible in general caused by the process of destruction or modification of a functional group or more is contained in the enzyme molecule. While the barriers can be either reversible competitive or not competitive barriers.
Barriers to compete because there is a molecule similar to the substrate, which can also form complexes, the enzyme inhibitor complex (EI). Obstacles are not competing are not influenced by the amount of substrate and inhibitor concentrations that do it.
In the multi-enzyme system is usually the first enzyme in the sequence is the enzyme controlling or commonly referred to as regulatory enzymes. There are two kinds of regulatory enzymes that control is not covalent (allosteric enzymes) Allosteric enzyme in addition to having the catalytic substrate binding to the regulator also has a functioning governing metabolite binding substance.
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