Tyrosine Essay

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Enzyme Action: Experiment with Tyrosinase Background The purpose of this laboratory is to introduce students to the quantitative measurement of enzyme activity by using the, enzyme, tyrosinase from a potato. Tyrosinase is found in many plants and animals where it is responsible for a biochemical pathway beginning with the amino acid, tyrosine, (hence the name “tyrosinase”) and leading ultimately to the formation of melanin, a black pigment. Activity of this enzyme in part accounts for the darkening of skin in response to sunlight and the darkening of a freshly peeled potato (or banana, apple, or pear) when exposed to air. The specificity of tyrosinase for the substrate tyrosine is not great. It will, in fact, react with a variety of ring structures including its natural substrate, tyrosine, with one hydroxyl group, and catechol, a phenol with two hydroxyl groups. [pic] In the experiments below catechol is used as an artificial substrate for tyrosinase. In the presence of this enzyme catechol is oxidized to ortho-quinone, which immediately undergoes secondary reactions leading to the formation of strongly colored products. The formation of these products is very rapid and their measurement over time indicates the rate of enzyme activity. [pic] Question What is the rate of product formation during the first ten minutes of a reaction between the enzyme tyrosinase and the substrate catechol? (Assume that both the enzyme and substrate are present in high concentrations.) Materials Test tubes Spectrophotometer 20 Potato enzyme (tyrosinase) Catechol (0.006 M) Phosphate buffer (0.1 M) Distilled water Procedure A. Tyrosinase: was prepared from potato immediately before the laboratory by the following procedure: 1. A medium sized (150-200 grams) potato was

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