Q17 - Glucose Oxidase and Enzyme Kinetics

Theoretical 2 Real exam question - full text reproduced under IBO's CC BY-NC-SA 4.0 license

The Michaelis-Menten equation describes the relationship between substrate concentration ([S]) and enzymatic reaction rate (v).

K_m = the Michaelis constant, which is the substrate concentration at which v = ½V_max and represents the affinity of enzymes to particular substrates.

V_max = the maximum rate in a given reaction mixture.

Glucose oxidase catalyses the oxidation of glucose (MW 180 g/mol) to glucono-1,5-lactone, while O₂ is reduced to H₂O₂. For glucose oxidase K_m is estimated as 25 mmol/l.

Michaelis-Menten equation, plot, and glucose oxidase reaction scheme showing glucose meter strip operation

A reaction catalysed by glucose oxidase is used to measure blood glucose concentration. A glucose meter is actually an electric current meter. The blood sample is applied to a strip containing immobilized glucose oxidase, and the meter records the flow of electrons accompanying the oxidation of H₂O₂ catalysed by a non-enzymatic catalyst contained in the meter strip.

True or False?

Q17.1. Among isoenzymes with the same Vmax value but different Km values, the enzyme with the lowest Km value has the highest affinity for the substrate.

Q17.2. For the meter to accurately measure blood glucose concentration, the glucose oxidase used should have a broad substrate specificity.

Q17.3. For the meter to accurately measure blood glucose concentration, the reaction on the strip should be in the P-Q range of the substrate concentration.

Q17.4. The two-step reaction presented in Fig. III is essentially irreversible in these conditions.

Q17.5. An acidic buffer facilitates oxidation of H2O2.

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Question reproduced from IBO 2023, Theoretical Paper 2, licensed under CC BY-NC-SA 4.0 - attributed to the International Biology Olympiad. Open the full exam PDF