BIOS 2011 Lab 1 Enzymes

Succinic dehydrogenase is one such enzyme our succinic

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Unformatted text preview: me enzymes have only one substrate, while others have two or more, and likewise the number of products vary. Some enzymes utilize substrate coupling, combining the energy produced by one exergonic reaction to drive an endergonic reaction. Such enzymes require both substrates in order to perform their activity and produce more than one product. Succinic Dehydrogenase is one such enzyme. Our Succinic Dehydrogenase in this lab comes from homogenized calf (Bos taurus) heart cardiac muscle tissue. It is a protein that is one of the enzymes in the Tricarboxcylic Acid Cycle (also called the TCA Cycle or Krebs Cycle) and is located in the mitochondria of eukaryotic cells, anchored to the inner mitochondrial membrane. Succinic Dehydrogenase couples the oxidation of Succinic Acid to the reduction of Flavin Adenine Dinucleotide (FAD) and produces two products, Fumaric Acid and FADH2 as shown below (Figure 1). Figure 1: Equation for the activity of Succinic Dehydrogenase Specifically, the Succinic Dehydrogense dehydrogenates succinic acid by transferring two electrons and two protons to FAD, in the process creating the double bond in the fumaric acid. FAD is reduced to form FADH2, one of the important energy currency molecules, like NADH2, that cells use to temporarily store high ­energy electrons. FADH2 then goes into the mitochondria’s electron transport chain to be used for producing ATP, the most widely used energy currency molecule in the cell. 3 Exercise 1 Enzymes We will be studying the phenomenon of competitive inhibition using Succinic Dehydrogenase as part of our laboratory model. Competitive inhibition is one of the two major types of inhibition that can slow the activity of enzyme solutions. Competitive inhibition is caused the enzyme’s active site binding to a molecule that is not the substrate, but is similar in shape and charge to the substrate. This is unlike allosteric inhibition where inhibition occurs because of a conformational change to enzyme molecules when a molecule binds to a second site that is not the active site of the enzyme. An inactivated allosteric enzyme has a disrupted active site that no longer has a functional shape. Figure 2: Chemical Structures of Succinic Acid and Malonic Acid Malonic Acid acts as a competitive inhibitor of Succinic Dehydrogenase because it is similar in shape and charge to the succinic acid substrate. Thus it easily fits to the Succinic Dehydrogenase active site. But lacking two adjacent CH2 groups in its chemical structure, malonic acid can neither be dehydrogenated nor used for the reduction of FAD. It will simply bind to Succinic Dehydrogen...
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