Enzymes are biological molecules - typically proteins - that act as catalysts. They speed up chemical reactions within cells by lowering the activation energy required for the reactions to occur. Limitations of using enzymes include: 

• While enzyme specificity is an advantage for targeted reactions, it limits their use in certain processes. 
• They are sensitive to changes in pH and temperature. Too high temperatures or extreme pH can denature or deactivate enzymes permanently. 
• Enzymes are susceptible to degradation over time, which compromises their activity and efficiency.