In every living cell, there are many reactions taking place in order for it to conduct necessary functions. To speed up the rate of these reactions, enzymes are necessary because they lower the activation energy of the reaction without getting used up or changing the products being formed. Enzymes are mostly proteins and their catalytic activity depends heavily on their shape. Therefore, each enzyme is specific to the substrate they will bond to. A substrate is the material the catalyst reacts to and binds to the active site of the enzyme, which forms the enzyme-substrate complex (Giles and Carter, 2011). Enzyme activity can be affected by factors such as pH, temperature, and other specific chemicals. For example, chemicals that may block enzyme activity are inhibitors. There are two types of inhibition, competitive inhibition, which is when a molecule and the substrate are similar in structure and compete for the binding to the active site of enzyme, and noncompetitive inhibition, which is when the inhibitor binds to another place on the enzyme and causes the enzyme to lose its catalytic properties (Giles and Carter, 2011). In this experiment, we investigated the inhibition of the enzyme catechol oxidase by the inhibitor phenylthiourea (PTU). By having one control tube and two experimental tubes, one with an increased concentration of catechol, the enzyme activity of catechol oxidase can be observed. This was done to decide whether PTU was a competitive or noncompetitive inhibitor of catechol oxidase.
Materials and Methods
Three tubes were obtained. First, 5 mL of distilled water was added to each tube. Then, 0.5 mL of potato extract was also added to each tube. PTU was then only added to the first two experimental tubes as the third tube is a control. 0.5mL of distilled water was added to the first experimental tube, while 1 mL was added to the third (control) tube. Lastly, catechol was added to each tube, with 0.5 mL in the first and third tube, and 1mL in the second experimental tube.
Each tube was then covered with fresh Parafilm and mixed. After the solutions were mixed well, the color of the mixture was observed. The color change of the mixture manifested how the enzyme catechol oxidase was affected by the inhibitor PTU.