The inhibition of catechol oxidase by lead

This practical exists in two different versions. One is designed specifically for Scottish Highers, and is in the appropriate format. The other is in a standard format suitable for use across the UK.

The enzyme, catechol oxidase, is easily extracted from banana. This enzyme is responsible for turning fruit brown. It is a two step process. Lead inhibits the catechol oxidase. This inhibition can be measured if the reduction in melanin production is quantified using a colorimeter or a SAPS colour chart.

In this practical, students extract the catechol oxidase from banana and mix it with varying concentrations of lead which is thought to inhibit the enzyme. A control tube will also be present. The experiment is carried out in the presence of a buffer solution. Such solutions are used to try and prevent changes in pH. Measuring the intensity of the brown colour formed at the end of the experiment will indicate how active the enzyme is and thus how much the volume of lead added has inhibited the enzyme.