Enzymes

Temperature

As temperature increases, the kinetic energy of molecules also rises, leading to more frequent and energetic collisions between enzyme and substrate molecules. This generally increases the reaction rate up to an enzyme’s optimum temperature, which is around 37°C for human enzymes.

Above Optimum Temperature: If the temperature rises above the optimum, the enzyme’s structure, particularly the active site, begins to denature. Denaturation disrupts the hydrogen bonds and other interactions that maintain the enzyme’s shape, causing a loss of activity as the enzyme no longer fits the substrate properly.

Below Optimum Temperature: At low temperatures, enzyme activity is reduced because molecules move more slowly, resulting in fewer collisions between the enzyme and substrate.

Optimum Temperature: The enzyme operates at its highest efficiency, with the most effective rate of substrate binding and conversion to products.

pH

Enzymes have an optimal pH range in which they function best, often depending on their natural environment within the body. For example, pepsin in the stomach works optimally at a highly acidic pH of around 2, while enzymes in the blood, like amylase, function best at a neutral pH of about 7.

Below or Above Optimum pH: Deviation from the optimal pH can disrupt the ionic and hydrogen bonds that maintain the enzyme’s three-dimensional structure. Extreme pH levels can lead to denaturation, altering the shape of the active site and reducing enzyme activity. Even slight changes can affect the charges on amino acids in the active site, affecting substrate binding.

Presence of Inhibitors

Inhibitors are substances that reduce enzyme activity by interfering with the enzyme’s ability to bind to its substrate. There are two main types:

Non-Competitive Inhibitors: These inhibitors bind to a different site on the enzyme, causing a conformational change that affects the active site, making it less effective or completely non-functional. Unlike competitive inhibitors, their effect cannot be reversed by increasing substrate concentration, as they do not compete directly with the substrate.

Competitive Inhibitors: These molecules resemble the substrate and compete for the active site, blocking substrate access. While they do not permanently damage the enzyme, they decrease the reaction rate by reducing the number of available active sites. The effect of competitive inhibitors can often be overcome by increasing substrate concentration.

Substrate Concentration

The concentration of the substrate affects enzyme activity, influencing how quickly products are formed.

Saturation Point: When all active sites are occupied, the enzyme reaches its maximum activity (Vmax), and further increases in substrate concentration have no effect. The enzyme is working at full capacity, and the rate of reaction is limited by the availability of active sites, not substrate molecules.

Low Substrate Concentration: At low concentrations, enzyme activity increases steeply with substrate concentration because more active sites are available than substrate molecules.

Increasing Substrate Concentration: As substrate concentration rises, enzyme activity increases since more substrate molecules are available to bind with active sites. However, this continues only up to a point.