Factors Affecting Enzyme Activity

Factors Affecting Enzyme Activity

The rate at which an enzyme works is not fixed - it changes with the conditions around it. The main factors that influence enzyme activity are temperature, pH, the concentration of the substrate, the concentration of the enzyme itself, and the presence of other molecules that help or hinder the enzyme, such as co-factors, activators and inhibitors. Two of these factors - temperature/pH and substrate concentration - are important enough to be looked at in their own right in the sections that follow; the effect of inhibitors is considered here.

An inhibitor is a molecule that reduces or stops an enzyme's activity. Competitive inhibitors have a shape similar enough to the normal substrate that they can occupy the active site themselves; because the inhibitor and the substrate compete for the same site, adding more substrate can outcompete the inhibitor and restore activity. A classic example is malonate, whose structure resembles succinate closely enough for it to bind the active site of the enzyme succinate dehydrogenase and block succinate from being processed. Non-competitive inhibitors, by contrast, bind at a site distinct from the active site; this binding distorts the enzyme's shape so that it can no longer catalyse the reaction properly, and because the inhibitor does not compete for the active site itself, simply adding more substrate cannot reverse the effect. Heavy-metal ions binding at such alternate sites are a typical example of non-competitive inhibition. …