Effects of Substrate Concentration

We examined reaction rate at different substrate concentrations. Our standard tubes contained 1 mL of hydrogen peroxide, and different groups ran reactions with more or less substrate to compare to that. Because each group tried different volumes of substrate, we got extremely variable results which proved difficult to interpret. In general, with much less substrate we got slower reactions and with more, we got faster reactions. What we expect to see is that the rate should level off once it reaches the maximum (when every peroxidase enzyme has a hydrogen peroxide molecule to interact with -- at that point, adding more hydrogen peroxide can't increase the reaction rate because all of the available enzymes are busy).

Effects of Enzyme Concentration

We also examined reaction rate when we increased the amount of turnip extract in our tubes. Since the turnip extract contained our peroxidase enzyme, this increased the enzyme concentration in our reactions. The graph above shows that as we increased the amount of enzyme in the tubes, our reaction rate increased. At some point, the maximum raction rate should be achieved and we should see the curve level off (see the substrate concentration curve above for an example), but based on this data, more than 3 mL of turnip extract is required to reach a 1:1 ratio of enzyme to substrate molecules.

Concentration Effects Summary

Enzyme reaction rates have set limits: they can't drop past zero (no reaction) and they can't speed up past 100%. When there is a 1:1 ratio of enzyme and substrate, the reaction is going as fast as it can. Add more enzyme, and there won't be substrate for it to react with. Add more substrate and there won't be enzyme free to work with it. Thus, when adding either substrate or enzyme, you should expect to see the see the reaction rate curve level off when the maximum is reached.