Factors that affect enzyme action

External Factors Influencing Enzyme Action

Temperature: Enzymes work best at an optimum temperature, usually around body temperature (37°C) for human enzymes. Above this, the enzyme’s structure begins to break down (denature), causing a rapid decrease in activity.
pH: Each enzyme has an optimum pH at which its active site best fits the substrate. Deviation from this pH alters the enzyme’s shape, resulting in reduced activity or denaturation. For example, pepsin, a stomach enzyme, has an optimal pH of about 2, while trypsin, an enzyme in the small intestine, functions optimally at a pH of about 7.5.
Substrate Concentration: An increase in substrate concentration leads to an increase in rate of reaction, as there are more substrate molecules available to collide with enzyme molecules, until a saturation point where all enzyme’s active sites are occupied. At saturation point, further increase in substrate concentration has no effect on the rate of reaction.

Internal Factors Influencing Enzyme Action

Enzyme Concentration: If the substrate concentration is kept constant, increasing the enzyme concentration will increase the reaction rate. This is because there are more active sites available to catalyse the reactions.
Inhibitors: These are substances that reduce enzyme activity. They may act competitively, by blocking the active site, or non-competitively, by binding to an area other than the active site, causing a conformational change in the enzyme which prevents it from binding with the substrate.
Co-factors and Co-enzymes: Co-factors are non-protein substances that help an enzymatic reaction proceed efficiently. They may be integral parts of the enzyme molecule (as with many metal ions) or may be loosely associated with the enzyme (as with co-enzymes). They assist in the transfer of certain types of groups between substrates.
Enzyme Modifications: Many enzymes can be activated or deactivated by post-translational modifications, such as phosphorylation or methylation. These modifications often change the shape of the enzyme, hence affecting its ability to bind to its substrate.