Enzymes are made up of proteins, which are the biocatalysts of the human body. Enzymes play a key role in increasing the rate of biochemical reactions by lowering the activation energy. Kuhne coined the term enzyme. The first enzyme Zymase was discovered by Buchner. Northrop and Summer established the proteinaceous nature of the enzymes. In this article, we will study the enzyme properties in detail.
The general properties of enzymes are:
The monomer unit of an enzyme is an amino acid. All known enzymes are proteins. They are made up chains of amino acids linked together by peptide bonds.All enzymes are protein except ribozymes which are RNA molecules. All enzymes like any protein have primary, secondary, tertiary structure. In its tertiary structure, polypeptide chains fold to form small cavities or pockets known as “active site”, substrate binds at active site.
Ribosomes synthesise the enzymes. By the one-gene-one-polypeptide hypothesis, if an enzyme is made up of polypeptide chains, those are synthesised by the same gene. But, on the other hand, if an enzyme comprises different kinds of polypeptide chains, those are synthesised by different genes. For example, cytochrome oxidase, Rubisco, and Nitrogenase.
Enzymes are large-sized biomolecules with high molecular weight and more surface area. As a result, they have more active sites. As a result, many substrates are converted into products by one molecule of the enzyme at a time. For example, the enzyme pyruvate dehydrogenase complex helps in respiration reaction and has the highest molecular weight.
The common range of temperature for enzyme activity is 20-40oC. Enzymes work on the temperature of the body of an organism, not depending on the temperature of the environment. The plant enzymes are affected by environmental temperature change, as the plant does not show homeostasis. Enzymes become denatured at high temperatures and become inactive at low temperatures.
Enzymes show high specificity over pH, temperature, and substrates. The enzyme’s common pH range would be 6-8. Each enzyme has its specific ph value.
Every enzyme works on a specific substrate that binds at the enzyme’s active site. It is made of a particular sequence of amino acids and recognises the substrate. For example, the action of pyruvate dehydrogenase on pyruvic acid, the action of succinic dehydrogenase on succinic acid.
It depends on activation energy, where the minimum amount of energy is more than the free energy of reactants. It is required to reach the chemical reaction’s transition state and undergo the reaction.
Reactant molecules are converted into products by one enzyme molecule in a unit of time. For example, the carbonic enzyme anhydrase has the highest T.O.N.
Enzymes provide an alternative pathway for a reaction with lower activation energy. The activation energy is the minimum energy input needed for the response, and the substrates are converted into products.
The transition state is where molecular enzymes intermediate between the substrate and its product in which the reaction passes.
The rate-limiting step of any reaction is the slowest, which converts the enzyme-substrate complex to the product. The reaction rate will be directly proportional to the concentration of the E.S. complex.
There are three phases of enzyme kinetics of a reaction:
The concentration of enzyme substrate complexes forms a rapid burst. The reaction rate is slow, and gradually the enzyme-substrate complex speeds up to grow.
The enzyme-substrate concentration remains constant and is quickly formed as it is broken down. The rate of the reaction is faster than in the pre-steady state.
The substrates deplete, and a few enzyme-substrate complexes would be formed. The rate of the reaction is slow in a post-steady state.
Enzymes follow the Michaelis-Menten reaction kinetics. As the concentration of the substrate increases, the catalytic activity of the concentration of an enzyme will increase to the maximum rate Vmax. The substrate concentration at which the chemical reaction attains half of its maximum velocity is called the Michaelis-Menten constant (Km).
It represents the concentration of the substrate at which the rate of enzymatic reaction becomes half of the maximum velocity or acceleration. If an enzyme passes through the high Km constant, the substrate affinity would be low. As a result of this, the reaction rate will also be low.
The Michaelis- Menten Kinetics equation is given by:
V = Vmax[S] / Km + [S]
Where V is the initial reaction rate of the reaction
[S] is the initial substrate concentration.
In steady state, the concentration of enzyme-substrate complexes is constant.
Simple enzymes are made up of only protein molecules. For example, Trypsin, Pepsin
Conjugated enzymes are made up of both protein and non-protein parts. The non-protein parts include the coenzymes, metal activators, and prosthetic group.
Coenzymes are organic, non-protein parts of the enzymes. It is loosely attached to apoenzymes. They are made up of vitamins.
When a non-protein part is tightly or firmly attached to apoenzymes.
Metal activators are loosely attached to an inorganic co-factor. They are also called metallic factors or co-factors. For example, Fe, Co, Mn, Ca, Mg.
The polypeptide chain comprises a specific sequence of amino acids at which the particular substrate is bound and catalysed. This site is called an active site. Genetic codes can determine the very specific sequence of amino acids.
Allosteric sites are the sites where the chemical other than substrate is bound. Therefore, these enzymes are called allosteric enzymes. For example, Phosphofructokinase, Hexokinase.
Enzymes are the middle man of reactions. In this article, we have read about the properties of enzymes with enzyme kinetics in detail. The structures of enzymes like simple and conjugated are clearly explained.
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