Classification
In the past, enzymes were usually named after the substrate they act upon (amylase, maltase, protease, etc.) . The classification system used nowadays, devised in 1961 by the first Enzyme Commission (EC) of the International Union of Biochemistry (IUB), is based on the substrate as well as on the overall reaction catalysed by it the reaction. Every enzyme is classified with a code, prefixed by EC, containing four elements separated by points, and the system name depending on the catalysed reaction. Enzymes are divided in 6 main divisions or classes; the first part of the number indicates the class the enzyme belongs.
1. Oxidoreductases: Oxireduction reactions
2. Transferases: Transfer of functional groups
3. Hydrolases: Hydrolysis – a reaction that involves breaking a bond by means of H2O
4. Lyases:Non-hydrolytic breaking of a C-C, C-O, C-N bond or addition to a double bond
5. Isomerases: Balance between isomers
6. Ligases: Joining together of two molecules coupled with the hydrolysis
of a diphosphate bond in ATP or a similar triphosphate.
Taking an enzyme with following code as an example: .B.C.D., A refers to the class (catalysed reaction, ex. 4 lyases); B and C refer to the catalysing reaction, and identify the subclass and the subsubclass; D is the serial number of the enzyme in its subclass.
Enzymes kinetics
Catalysis kinetics is mostly regulated by the concentration of substrate. The estimation of the reaction rate might appear easy at first, but the catalysis reaction causes a decrease of the substrate concentration and an increase of the rate of reaction. The rate of reaction is regulated by a specific constant for the type of reaction, according to the formula according to which the rate of the fi rst reaction will be V = k1 [ E ] [ S ] (where E = enzyme and S = substrate). In enzyme-catalysed reactions, the typical turnover of each enzyme is defi ned, which corresponds to the constant k and represents the number of moles of substrate S that a mole of catalyst can convert into the product P per unit time. The rate constant also depends on the temperature. Following this principle, Michaelis-Menten (1913) developed an equation that relates the reaction rate of the product P to the concentration of the substrate[S]. The Michaelis-Menten constant is the concentration of substrate that permits the enzyme to achieve a reaction at half its maximum rate. It corresponds to following Scheme B – Mechanism of enzyme activity ratio KM = (k-1 + k2 ) / k1. The Michaelis-Menten constant is an approximation of the affi nity of each enzyme for a substrate based on the rate constants within the reaction: The lower the value for KM, the lower will be the substrate concentration that allows to reach a reaction rate corresponding to half the maximum speed, which means a high affinity between enzyme and substrate. Vice versa, a high value for KM, requires a higher substrate concentration to reach a reaction rate corresponding to half the maximum speed, which means a lower affinity between enzyme and substrate. In some cases, enzyme activity may differ from this kinetic model for various reasons: The enzyme does not adequately break down in the substrate, or the high concentration of fat in the substrate limits its functions, as well as high sugar concentrations may inhibit amylases. Enzyme activity is pH sensitive, as it alters the protein conformation as well as its ionic charge. Therefore, an optimum pH produces a reaction rate of Vmax. Enzyme activity is also temperature sensitive: There is an optimum temperature at which the enzyme performs its activity at best, and a denaturation temperature at which the enzyme starts becoming inactive.
Enzymes production
Most industrial enzymes are obtained from the fermentation of micro-organisms (bacteria, fungi) and the purification of the fermentation solution. Submerged fermentation is the most widespread method to produce enzymes. The microbial strain used for industrial production must express the required enzyme activity. It cannot have pathogenic properties nor produce toxins. To improve strain properties, the micro-organism must be genetically stable. The purity of the strain must be checked accurately. Fermentation water must contain an adequate enzyme concentration in order to guarantee the required performance. The enzyme is then recovered and purified according to the intended application. Losses in enzyme activity should be limited to the minimum. The fermentation of these micro-organisms, in specific situations, allows the synthesis and liberation of a variety of enzyme activities, as required.
