Glucose oxidase (GOx) is a protein first found in fungi. It reacts with glucose and almost nothing else. Like all enzymes it is a catalyst, so one enzyme molecule can process many glucose molecules without being used up.
GOx is selective because its shape fits glucose like a lock fits a key.
THE REACTION
Glucose and oxygen in, peroxide out
Glucose oxidase converts glucose and oxygen into gluconolactone and hydrogen peroxide (H₂O₂). The hydrogen peroxide is the product an electrode can easily detect.
More glucose means more hydrogen peroxide, which means more electrical signal.
TWO HALF-STEPS
The enzyme gets reset
Step 1Glucose hands electrons to the enzyme's built-in FAD group, and glucose becomes gluconolactone
Step 2Oxygen takes those electrons back, which makes hydrogen peroxide
ResultThe enzyme is back to its starting state and ready for the next glucose
Oxygen acts as the natural electron acceptor in this reaction.
ALTERNATIVES
Other enzymes can do the job
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Glucose dehydrogenase
Does not need oxygen. Common in test strips, but some versions also react with other sugars
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Glucose oxidase
Very selective for glucose and well studied, but its oxygen dependence has to be managed
The right enzyme depends on where the sensor will be used.
ENZYME LIFETIME
Enzymes do not last forever
HeatHigh temperatures unfold the protein and destroy its shape
TimeEnzymes slowly lose activity, which limits how long a sensor works
ProtectionLayers around the enzyme, and careful storage, extend its life
Enzyme stability is one reason sensors are replaced every week or two.
UNIT 5 STUDY COMPLETE
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You've covered how glucose oxidase works and what limits it.