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Enzyme concentration affects the rate of the reaction.

The graph below shows that the rate or velocity (V) of a reaction depends on substrate (K) concentration up to a limit. KM is the substrate concentration midway to the maximum rate, and is a useful value to note since the reaction is non-linear, and return on substrate investment diminishes as we approach the maximum rate (Vmax). If the substrate is valuable, we can think of KM as the optimal amount of substrate to invest. If the substrate is inexpensive, then saturating the reaction with substrate ensures the most product in the shortest period of time. As we approach Vmax, more and more of the enzyme is involved with substrate, so no further increase in substrate concentration can speed the reaction further.

These changes are regulatedby catalytic reactions, which are regulated by enzymes.

With this type of inhibition, V will not change because V is a function of all enzyme molecules uniting with substrate (thus having no effective competition).

All of these reactions are enzyme-driven.

The effect of substrate concentration on the rate of enzyme-controlled reactions

If you plotted a graph of initial reaction rate against the concentration of a reactant, then there are various possibilities depending on the relationship between the concentration and the rate.

A water bath was heated to 35°C. 5cm³ of undiluted0.1% amylase solution was pipetted into one test tube and 5cm³starch into another. Both were stood in a water bath and left toreach the correct temperature. The solutions were then mixed, thetest tubes returned to the water bath and at one minute intervals adrop of the mixture was removed and tested with iodine solution ona white tile. The starch had been broken down completely when theblue-black colour (obtained by testing for starch with iodine)disappeared. This was repeated with the other enzyme concentrationsof 0.05%, 0.025% and 0.01% respectively.

The graph for enzyme controlled reactions looks like this:

A reminder about the effect of concentration on rate in ordinary chemical reactions

Dilution of enzyme could also reduce the speed of the reaction if the enzyme needs a critical cofactor or if the enzyme only works when grouped together (quaternary structure).

A graph of the relative reaction rate (1/time taken for a colourchange to occur) showed that, as the enzyme concentrationincreased, the reaction rate was faster. This was true up to thepoint at which the substrate was saturated with enzymes - at thispoint any higher enzyme concentrations gave no furtherincrease.

With reactions controlled by enzymes, you get a completely different type of graph.
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The effect of temperature on the rate of enzyme-controlled reactions

However, the rate at which enzymes work are affected by the following factors/variables: Concentration: In a more concentrated solution, collision occurs more often because there are more molecules....

Plotting rates of enzyme-controlled reactions against temperature

But as concentration increases, increasing the concentration more has less and less effect - and eventually the rate reaches a maximum. Increasing the concentration any more makes no difference to the rate of the reaction.

Diagram to show the reaction of specific enzymes 2

The reason for this is actually fairly obvious if you think about it. After a certain concentration of substrate is reached, every enzyme molecule present in the mixture is working as fast as it can. If you increase the substrate concentration any more, there aren't any enzyme molecules free to help the extra substrate molecules to react.

Each of these parametersaffects the rate of an enzyme reaction.

The catalytic site of the enzyme is empty, waiting for substrate to bind, for much of the time, and the rate at which product can be formed is limited by the concentration of substrate which is available.

The effect of pH on the rate of enzyme-controlled reactions

The rate of formation of product now depends on the activity of the enzyme itself, and adding more substrate will not affect the rate of the reaction to any significant effect.

This increases the concentration and thus the rate of reaction.

By carefulmanipulation of the salt concentrations, we can producefractions which contain purer solutions of enzymes, or atleast are enriched for a given enzyme.

Increasing Substrate Concentration increases the rate of reaction.

This is usually expressed as the Km (Michaelis constant) of the enzyme, an inverse measure of affinity.

For practical purposes, Km is the concentration of substrate which permits the enzyme to achieve half Vmax. An enzyme with a high Km has a low affinity for its substrate, and requires a greater concentration of substrate to achieve Vmax."

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