1. Temperature: Enzymes have an optimal temperature at which they function best.

* High temperatures: Can cause the enzyme to denature (lose its shape) and become inactive. This is because heat disrupts the weak bonds that hold the enzyme's structure together.

* Low temperatures: Slow down enzyme activity, but usually don't cause permanent damage. The enzyme can regain its function when the temperature returns to optimal levels.

2. pH: Enzymes also have an optimal pH range.

* Extreme pH: Whether too acidic or too basic, can disrupt the ionic bonds that hold the enzyme's structure together, leading to denaturation and loss of activity.

Remember, these are just two examples. Other factors like the presence of inhibitors, activators, or even substrate concentration can also influence an enzyme's shape and activity.