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Mdh Assay Lab Report

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Enzymes are biological catalysts, usually made up of protein molecules that act on one or more specific substrates, converting them to products with different molecular structures. Malate Dehydrogenase (MDH) is one example of an enzyme that catalyzes oxaloacetic acid and NADH into malic acid and NAD+ as part of the citric cycle. In order to perform the MDH assay, a solution of pure MDH was collected from bovine heart. A control assay was performed, along with three experimental groups to test concentration, pH, and temperature. Units of activity were calculated and showed that all three variables have an effect on enzyme activity. MDH was shown to have an optimum pH, concentration, and temperature at which enzyme activity was at its highest …show more content…

A control sample was taken so that it could be compared to the different experimental groups (enzyme concentration, pH, and temperature). The conditions used for the control sample were a MDH concentration of 1X, a pH of 7.5, and a temperature of 25 oC. The control solution was prepared in a cuvette with 10 μL oxaloacetic acid, 1.0 mL of phosphate buffer, and 10 μL NADH. The control sample was placed in the spectrophotometer in order to confirm that the original absorbance was above 0.6. There were then 10 μL of enzyme added to the solution and the spectrophotometer ran for one minute while the change in absorbance was recorded, giving the slope of the reaction rate. After completing the assay for the control, a set of assays was performed to test the effects of varying enzyme concentration, pH, and temperature on the reaction rate. The assay to test concentration was done by taking the original 1X solution of MDH and diluting the sample down to 0.5X and 0.25X. After completing the dilutions, the same steps done in the control assay were followed. The assays to test pH were performed using buffers with a pH of 4 and a pH of 10 and then using a spectrophotometer to record the data. Lastly, the effects of temperature on the reaction rate were tested by measuring three samples at varying temperatures. The three samples were tested in: a -1 oC ice bath, a 37 oC bath, and the third was …show more content…

It was hypothesized that as the enzyme concentration increases, the reaction rate increases. Also that as the pH moves away, both increasing and decreasing, from the optimum pH (7.5) the reaction rate decreases. Lastly, as the temperature moves away, both increasing and decreasing, from the optimum temperature (37 oC) the reaction rate decreases. All of the results, as described below, were consistent with the hypothesis that was made. As the results show in Figure 1, as the concentration of enzymes is increased, the units of activity also increased with the maximum being 0.0622 µmol/min at 1X concentration. This may be because when the enzyme is in a higher concentration there is more catalyst present, causing the reaction rate to increase. As Figure 2 shows, altering the pH, either higher or lower, had a negative effect on the reaction rate. This indicates that the optimum pH for this reaction is approximately 7.5, giving a rate of 0.0622 µmol/min. It is possible that altering the pH to extreme highs or lows causes the configuration of the enzyme to be altered and inhibits the biochemical system. The results also show that temperature has an affect on the reaction

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