Answer to Question #125202 in Biochemistry for Amuda Manikandan

Question

In a procedure for testing blood glucose, a drop of blood is placed on a paper strip impregnated with the enzyme glucose oxidase and all the reagents necessary for the reaction.
The H2O2 produced causes a color change on the paper that indicates how much glucose is present. Since glucose oxidase is specific for the beta anomer of glucose and doesn’t act on alpha anomer, in spite of this specificity, the reaction is used in a clinical assay for measuring total blood glucose which consists of a mixture of beta D glucose and alpha D glucose. Explain how this assay is effective in measuring total blood glucose

Answer 1

Blood glucose levels are measured by a procedure based upon the enzyme glucose oxidase.

Since the enzyme is used, it is very specific for D- glucose, and will not be subject to interferences from other molecules in the blood.

Glucose can be oxidized since it is a reducing sugar. Glucose oxidase enzyme catalyzes the oxidation of beta-D-glucose to D-gluconic acid. The alpha-D-glucose is converted to the beta form so that all of the glucose is measured at one time.

Diatomic oxygen from the air is the oxidizing agent acting upon the glucose reducing agent. During the reaction process the ring opens and the aldehyde on carbon is converted to D-gluconic acid. At the same time the oxygen in the presence of water is converted to hydrogen peroxide. So far all of the chemicals are colorless, so you would not be able to see the reaction taking place. We will now detect its color.

In most cases, hydrogen peroxide reacts with a second color producing chemical. For instance 2-methylaniline reacts with the hydrogen peroxide using an enzyme called peroxidase to produce a color forming chemical.

Concentration of the glucose is related to the intensity of color produced because the more the intensity, the higher the concentration of glucose. Therefore a simple color chart can be used to "read" the concentration of the glucose.