- Any condition that affects the three-dimensional shape of an enzyme will effect its activity.
- Two such factors that affect enzyme activity are temperature and pH.
- The shape of a protein is determined by its hydrogen bonds. Hydrogen bonds are easily disrupted by temperature changes. For example, most higher mammals have enzymes that function best within a relatively narrow temperature range between 35°C and 40°C. Below 3SX. the bonds that determine protein shape are not flexible enough to permit the
shape change necessary for substrate to tit into a reactive site.
- Above 40°C, the bonds are too weak to hold the protein in proper position and maintain its shape.
- When proper shape is lost, the enzyme is destroyed, this loss of shape is called denaturation.
- The enzyme action is like a ‘lock-and-key’ fit.
- Most enzymes also have a pH optimum, usually between 6 and 8. For example, when the pH is too low, the H+ ions combine with the R-groups of the enzyme’s amino adds, reducing their ability to bind with substrate.
- Acid environments can also denature enzymes. That is why some enzymes function at a low pH. For example, pepsin is the enzyme found in the stomach of mammals and has an optimal pH of approximately 2.
- Conversely trypsin is active in the more basic medium (pH 9) and found in small intestine. Overall the pH optimum of an enzyme reflects the pH of the body fluid in which the enzyme is found.