Properties of Enzymes
Presence of Species Specificity
Macromolecules including proteins differ in different species i.e.
they are species specific. It is attributed that the phylogenetic development which has given rise to microbiological variation is caused by variation in these molecules. Enzyme types (protease, a-amylase, lactase) which are found in many species will have properties which vary as much as the other properties of the organisms, for example, protease of two closely related species differs in several ways inspite of some similarities (Aunstrup, et al.
1979).Variation in Activity and Ability
Most of microbial enzymes applied in various ways are extracellular in their origin; they are influenced externally by temperature, pH, etc. However, their optimum stability and activity are very much close to optimum conditions for microbial growth. For example, optimum pH and temperature for amylase activity of a thermophilic microbial species e.g. Bacillus coagulans
differ from that of mesophilic species of some microbe (B. licheniformis).
Unlike extracellular enzymes, the intracellular enzymes are little influenced by external environmental factors.
Activity and stability of enzymes also differ. Xylose isomerase is stable at pH range from 4.0 to 8.5 but shows optimum activity at pH between 5.5. to 7.0. Similarly, temperature also influences enzyme activity.
On increasing the temperature enzyme activity gradually increases, but at certain stages temperature inactivates the rate of reaction and finally enzyme is denatured (at high temperature) as it is proteinaceous in nature. Thermal stability in the target enzyme may be a useful attribute during production of enzyme itself as heat may be used to destroy contaminant enzyme activity (Trevan, 1987). In addition to pH and temperature, the stability of enzyme is also increased by many factors such as : (a)
high concentration of respective enzymes (as protein aggregates and protects them), (b)
presence of their substrate and/or product (e.g.
amylase shows more stability in the presence of starch than in its absence), (c)
presence of ions (e.g.
a-amylase is denatured within 4 h in the absence of Ca++
), and (d)
reduced amount of water content in reaction mixture (for example, at natural conditions b-glactosidase results in production of glucose and galactose from hydrolysis of lactose in whey. But the same enzyme produces some glucose and galactose and mixture of trisaccharides from the same concentrated whey.Substrate Specificity
Organic matter contains the various constituents such as cellulose, hemicellulose, lignin, etc. in a complex matrix. In nature these are decomposed and mineralized by a variety of microorganisms. However, it is not possible for a single microbe to decompose all the constituents. For example, a cellulose decomposer will fail to decompose the lignin because of the presence of only cellulose. Therefore, on the decomposing materials community dynamics of microorgnasims i.e.
changing community of microbes with time exists till the disappearance of complex organic matter.
It is also possible that a particular microbe develops potentiality to secrete an enzyme in higher amount and utilize the substrate more rapidly than others. This inherent capacity makes the microbes capable to compete in the microbial competition for substrate utilization. Due to possession of this activity i.e.
high enzyme producing ability, exploitation of microorganisms is done. For example, Trichoderma reesei
secretes cellulase in high amount; therefore, this fungus is used for commercial production of cellulase.Activation and Inhibition
Some enzymes obtained from different sources show difference in responses to a given activator of inhibitor. For example, b-galactosidase isolated from fungi does not require cobalt, whereas the same of bacterial origin requires cobalt as a confactor. Thus cobalt activates b-galactosidase isolated from bacteria and inhibits it when obtained from fungi. Examples of some activators of enzymes used commercially are : proteins (for proteases), starch (for a-amylase), cellulose (for cellulase) and pectin (for pectinase).