Enzymatic Activity of Salivary Amylase
Abstract: Salivary amylase is an enzyme that can digest starch molecules and break them down to sugar molecules. In this experiment, the enzymatic activity and specificity of salivary amylase was examined depending on the changes in pH and temperature. In the first part of the experiment, the effect of temperature was determined, using constant temperature bath (4, room temp, 37, 50, 60, and 70°C). Having the room temp and 50°C as the highest and 37°C as infinite. In the second part of the experiment, the effect of pH was examined. Using the buffered solutions: acetate solutions (pH 4 and 5), phosphate buffer (pH 6.7 and 8), and bicarbonate buffer (pH 10). The results were recorded having all of them as infinite. Keywords: enzyme, infinite, pH, temperature, salivary amylase, starch
Enzymes are proteins that catalyze or speed up the rate of chemical reactions. Like all catalysts, enzymes work by lowering the activation energy for the reaction, thus dramatically increasing the rate of reaction. As with all catalysts, enzymes are not consumed by the reactions they catalyze nor do they alter the equilibrium of these reactions. All known enzymes are proteins, they are high molecular weight compounds made up principally of chains of amino acids linked together by peptide bonds. See Figure 1.
Figure 1. Typical protein structure – two amino acids joined by peptide bonds
Enzymes require the presence of other compounds - cofactors - before their catalytic activity can be exerted. This entire active complex is referred to as the holoenzyme; i.e., apoenzyme (protein portion) plus the cofactor (coenzyme, prosthetic group or metal-ionactivator) is called the holoenzyme.
Figure 2. Haloenzymes – apoenzymes plus various types of cofactors
One of the properties of enzymes that make them so important as diagnostic and research tools is the specificity they exhibit relative to the reactions they catalyze. A few enzymes exhibit absolute specificity; that is, they will catalyze only one particular reaction. Other enzymes will be specific for a particular type of chemical bond or functional group. In general, there are four distinct types of specificity: •
Absolute specificity - the enzyme will catalyze only one reaction. •
Group specificity - the enzyme will act only on molecules that have specific functional groups, such as amino, phosphate and methyl groups. •
Linkage specificity - the enzyme will act on a particular type of chemical bond regardless of the rest of the molecular structure. •
Stereochemical specificity - the enzyme will act on a particular steric or optical isomer.
Enzymes are catalyst and increase the speed of chemical reaction without themselves undergoing any permanent chemical change. They are neither used up in reaction nor do they appear as reaction products. The basic enzymatic reaction can be represented as follows
where E represents the enzyme catalyzing the reaction, S the substrate, the substance being changed, and P the product of the reaction.
A theory to explain the catalytic action of enzymes was proposed by the Swedish chemist Savante Arrhenius in 1888. He proposed that the substrate and enzyme formed some intermediate substance which is known as the enzyme substrate complex. The reaction can be represented as:
If this reaction is combined with the original reaction equation, the following results:
The existence of an intermediate enzyme-substrate complex has been demonstrated in the laboratory, for example, using catalase and a hydrogen peroxide derivative. Knowledge of basic enzyme kinetic theory is important in enzyme analysis in order both to understand the basic enzymatic mechanism and to select a method for enzyme analysis. The conditions selected to measure the activity of an enzyme would not be the same as those selected to measure the concentration of its substrate. Several factors affect the...
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