Biology

Influence of Malonate and Sodium Fluoride on the Activity of Enzyme Succinate Dehydrogenase to Assess Inhibitors of Cellular Respiration

Thaovy Mai Tran

BI 151.5233 (Winter 2013)

Todd Tiano

03/25/2013

Introduction

Most organisms produce adenosine triphosphate (ATP) as a source of energy for cellular work, using cellular respiration. Cellular respiration is a process that involves glycolysis -breaking down glucose into two molecules of 3- carbon pyruvate, the Krebs cycle - oxidizing organic fuel derived from pyruvate-, and the electron transport chain - moving electrons through a series of protein complexes to generate ATP (Reece, et.al, 2011). The process of cellular respiration occurs in the Cytoplasm and the Mitochondria in plants and animals. In this process, many more ATP molecules are produced compared to alcoholic fermentation which is a process that releases energy in glucose to generate ATP in the absence of oxygen. Aerobic respiration produces 38 ATP compared to 2 ATP of alcoholic fermentation, which is respectively (Morgan, et. al, 2011). As part of cellular respiration, the Krebs cycle is a series of eight steps, each catalyzed by a specific enzyme. One enzyme used is succinate dehydrogenase which catalyzes the conversion of succinate to fumarate, thus loses hydrogen ions and electrons for use in generating ATP. It is important to know what inhibitors affect the activity of this enzyme which eventually will affect the whole process of cellular respiration. In this experiment, 1M Malonate( CH2(COO)22-) and 0.1M of Sodium Fluoride (NaF) ,were employed as inhibitors to the enzyme succinate dehydrogenase to assess their effect on cellular respiration. Malonate is a molecule that inhibits the oxidization of succinate. Besides that, Sodium Fluoride is the main ingredient that is commonly found in

References: Discussion Discussion If the succinate is broken, then the DPIP will become colorless faster. As shown by the data in Table 2 and Figure 1 above, the transmittance level increased time after time from 0 minute to 30 minutes. It means that both sodium fluoride and malonate inhibited the activity of the enzyme succinate dehydrogenase in the reaction to convert succinate to fumarate. They worked as competitive inhibitors by binding to the active site (the groove where the substrate binds) of the enzyme and compete with the substrate. The enzyme became unavailable to the substrate that leads to the decreasing rate of cellular respiration. Therefore, the stated hypothesis should be accepted. Results also prove that malonate work better in inhibiting the activity of the enzyme succinate dehydrogenase than sodium fluoride. As a result, the performance of succinate dehydrogenase in tube 2 with sodium fluoride was only 25%. In other words, sodium fluoride inhibited about 75% activity of the enzyme. As for tube 3 with malonate, the performance of the enzyme was 15% compared to tube 1. Malonate inhibited 85% of tube 3’s enzymatic activity. One possible explanation is that as a Krebs cycle intermediate, it may exert a protective role in minimizing reverse-electron transfer meditated production of superoxide by Complex I (the first step in the electron transport chain) (“Succinate Dehydrogenase,” 2012). Reference Morgan, Judith Giles and Carter, M. Eloise Brown. Investigating Biology (Laboratory Manual). 7th ed. 107- 121. 2011. Reece, Jane B., Urry, Lisa A., Cain, Michael L., Wasserman, Steven A., Minorsky, Peter V., and Jackson, Robert B. Campbell Biology. 9th ed. 152-171. 2011. Malonate inhibition of oxidation in the Krebs Tricarboxylic acid cycle. (Received for publication, October 26, 1948), from http://www.jbc.org/content/178/1/241.full.pdf. Sodium Fluoride , from https://www.neb.com/products/p0759-sodium-fluoride-fluoride