Catecholase is an enzyme that catalyzes a response to injury among many types of plants. Upon exposure to oxygen, catechol in plant cells is oxidized, and, with catecholase, produces benzoquinone. Benzoquinone is used as a protection against invasion and infection by microorganisms (Stegenga, 84). The oxidation reaction of catechol may be represented by the following equation: Catechol + ½ O2 Benzoquinone + H2O

Benzoquinone is a brown color, allowing for observations about its presence to be determined by use of a spectrophotometer that measures the absorbance of green light, and, therefore, the presence of reflected brown-orange light.

An initial procedure was used to test the conversion of catechol to benzoquinone. …show more content…
Tube 1 contained 2 mL catechol solution and 3 mL dH2O. Tube 2 contained 2 mL catechol solution, 2 mL dH2O, and 1 mL of enzyme solution. The enzyme solution was added last. Since the reaction progresses over time, adding the enzyme last allowed for an almost immediate measurement of its absorbance without preliminary reactions occurring. Tube 3 contained 5 mL H2O that acted as a calibration tube for the spectrophotometer. Since the absorbency of light is different between water and air, this calibration tube allowed for a baseline reading of liquid in the spectrophotometer so that the remaining test tubes could be compared accurately. A spectrophotometer was used to test the following procedure: first using a kimwipe on Tube 3, setting the absorbance to zero, and then quickly inverting Tubes 2 and 1, respectively, with Parafilm, wiping them with kimwipes, and recording their initial absorbency with the spectrophotometer. All of the tubes were then placed in a 25°C water bath. After 5 minutes, each tube was shaken in order to prevent the settling of the substrate in the test tube. After 10