And so that's how we know that Serene is the one that is involved in actually catalyzing the cleavage of the peptide bonds at these specific bulky hydrophobic amino acids. Now, the next question is what is the general description of the reaction mechanism that takes place inside the active sites? Well, basically, it's a two step catalytic mechanism. And we'll discuss the steps involved in much more detail in the next several lectures. In this lecture, we're simply going to paint a general description, a general picture of what takes place inside the active site and how Serene is actually involved in breaking and catalyzing those peptide bonds so we see that experimental data suggests that Chimotrypsin uses a two step mechanism to actually hydrolyze peptide bonds. Now, the way that scientists actually studied the reaction mechanism of Chimotrypsin is by using a special type of substrate molecule that once we react that substrate molecule with the activity, the product that is produced gives off a color.