Salt Concentration On Turnip Peroxidase Activity Biology Essay

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Enzymes are proteins that catalysis chemical reaction to its highest speed. They do so by lowering the activation energy. Enzymes contain an active site where a substrate, in this case, the hydrogen peroxide binds to it and breaks into water and oxygen. Salt concentration denatures the structure of the protein, therefore, causing the rate of the reaction to decrease. The main purpose of this study was to discover whether the salt concentration affects the rate of reaction. Turnip Peroxidases were used, known as enzymes which are found in plants and animals. The hypothesis was that as the salt concentration increases, the absorbance rate decreases. This study was completed by running test of four different percent salt concentrations, 0%, 5%, 10%, and 15%. Using 0.5ml of peroxidase, .02 ml Guaiacol, 0.2 ml hydrogen peroxide, and a pH 7 buffer. Perform two tests per tube for accuracy. Each tube was put in the spectrophotometer at 500nm. According to the data 15% salt concentration yield the highest absorbance.


Plants and animals contain enzymes. Enzymes are proteins that are not consumed in the chemical reactions, but rather it can speed up the reaction. Catalysis is an enzyme which is found almost in all living cells especially in eukaryote cells (Cummings, 2005). It main function is to break down the hydrogen peroxide. Hydrogen peroxide is just produce naturally in chemical reactions, but the cells have to get rid of it before it builds up in a large amount. A cell uses catalysis to break down the hydrogen peroxide into water and oxygen. Hydrogen peroxide will going to feed into the catalysis and it is going to break that down into two products (Cummings, 2005). It does that at very incredible rate. Basically, an enzyme contains an active site. This active site is part of an enzyme where there has a hole in it. The substrate will than fit into it. The substrate is hydrogen peroxide. The enzyme basically tugs on substrate and breaks it down. Enzymes are very important in the chemical reactions, without them the reaction will occur at the lower rate. There are two types of inhibition. Inhibition can either be competitive, that is where a chemical is blocking an active site or the allosteric, where the enzyme is actually changing the shape of its active site, unable the reaction to take place (Hosoya, 1960). An enzyme itself never changes its shape, only the active site does. However, its unique structure of protein under specific circumstances can easily be denatured. An enzyme needs to be in certain atmosphere to be more affective. One of the factors that can effect the enzyme reaction is salt concentration (Cummings, 2005). Salt concentration has to be in its intermediate state for an enzyme to work properly. For instance, if the salt concentration is too high, then the enzyme site will be blocked by the salt ions (Huystee, (1987). Therefore, it will lower the reaction activity rate. The main intention of this experiment was to figure out the salt concentration and its effect on enzymes. To perform this experiment, use the turnip peroxidases. Peroxidases are an enzymes found in plant and animal cells (Gjesing, 1985). Because salt concentration denatures the enzyme we did an experiment to see how the salt concentration would effect the reaction. It is believed that the increase in salt concentration will lower the absorbance rate of turnip peroxidases.


In this experiment, the solution materials that are needed to perform this lab are: Enzyme Solution: 5 g turnip blended into 500mL water (1% solution) and then filtered through a p2 filter, Substrate Solution: NaCl (0%, 5%, 10%, and 15%), Indicator Solution: Guaiacol, Buffer Solution: pH 7 buffer (distilled water), and Hydrogen peroxides. The list of supplies that are need is follows: a spectrophotometer, cuvette tubes, and micropipette.


Prepare a control test tube (called the “blankâ€Â), containing all of the ingredients: 0.5 ml of turnip peroxidase, 0.5ml pH buffer, .02 Guaiacol, and put 0.2 hydrogen peroxide last, except the NaCl. Then, obtain the four additional cuvette tubes and start adding 0.5 ml (0 to 15%) of NaCl in each tube plus the same solution that control tube contains. Mix and put these tubes one by one in the spectrophotometer at 500 nm and record the absorbance every 15 seconds for 3 minutes. Repeat the trial for two times for each tube, then take the mean average.


The peak absorbance was at 15% concentrate (See Figure 2). After the concentration passed 15% the reaction slowed gradually.


As higher percent of salt concentration was added the absorbance increased. This happened because the salt concentration did not denature the enzyme (peroxidase), therefore, causing the enzyme to work its way out throughout until there was not enough enzymes to work with hydrogen peroxide. The data collected did not support the hypothesis because the absorbance peak was at 15% salt concentration. As assumed that the higher the salt concentration, the lower the absorbance would be. But that was not the case in this experiment. Salt concentration at 5 and 10% showed the lower peak, meaning that the presence of salt concentration actually lowered the reaction rate. It is the only 15% of salt concentration, where the peak was its highest. This could have happened because of the human error, miscalculation in finding the mean average, misreading the spectrophotometer or not having enough solution. If this experiment is to be repeated one of the question that should be addressed is what would happen if the higher than 15% of salt concentration was added, what would be the result?

Figure Legends and Figures

Figure 1. The Effects of Salt Concentration on Turnip Peroxidase Activity. Enzyme activity was measured using a spectrophotometer by recording the change in coloration of guaiacol to brown, indicating that hydrogen peroxide is complete.

Figure 2. The Effects of Salt Concentration on Turnip Peroxidase Activity. Enzyme activity was measured at the high peak of 15% salt concentration.

Literature Cited:

Campbell, Neil., Jane Reece (2005). Biology, 7th ed. Beth Wilbur. Benjamin Cummings

Publishing Menlo Park, California. pp. 150-157.

Gjesing, K.W( 1987). Plant peroxidases. The Febs Journal. 151: 497-504.

Hosoya, Toichiro (1960). Turnip peroxidase: Purification and physicochemical properties of

multiple components in turnip peroxidase. The Journal of Biochemistry. Vol. 47, No. 3.

Huystee, R. B (1987). Some molecular aspects of plant peroxidase biosynthetic studies. The

Journal of Plant Physiology. 38: 205-219.