Catechol Oxidase Lab Report

As mentioned before, browning in bananas is an enzymatic process where enzymes such as polyphenol oxidase serve as catalysts in the oxidation of several phenolic compounds. In this experiment however, the only reaction being tested is the oxidation of catechol (a diphenol) by the enzyme catalyst catechol oxidase or polyphenol oxidase, which initiates a chain of reactions and eventually triggers the formation of brown pigments known as catechol-melanins.
Catechol, also called 1,2-dihydroxybenzene is a phenolic compound with the chemical formula C6H4(OH)2. The catechol molecule consists of two hydroxyl groups bonded to a central benzene ring, hence the molecule is a diphenol (monophenols contain one hydroxyl group). Figure. below shows the
catechol oxidase, like several other enzymes and proteins, has a tertiary protein structure. This tertiary structure consists of several amino acid chains in shapes of pleated sheets and helices bonded together to form the long chain final complex structure of the enzyme. The pleated sheet and helix shapes arise from the formation of hydrogen bonds between the R groups* of various amino acids in the polypeptide chain. In order to function as an enzyme, catechol oxidase has an active site which consists of six histidine amino acids which chelate* two central copper ions to form a complex ion. The histidine amino acids form ligands as the lone pairs on the nitrogen atoms in their R groups form dative bonds with the two copper ions.
As for the browning process, the first step is the oxidation of catechol by the enzyme catechol oxidase. Two catechol molecules lose their two hydrogen atoms to the diatomic oxygen which subsequently forms two water molecule. Hence, the products of this reaction are two o-benzoquinone molecules and two water molecules. The following equation summarises this