In fact, inside our body, all the different enzymes have a Km value that range from about 0.1 molar to about tenths to negative seven molar. So we see that the Km value, the magnitude of the Km value, depends not only on the type of enzyme and the type of substrate, but it also depends on the conditions in the environment. So by changing, for example, the PH or the temperature of the environment, we can affect the value of Km. Now, what exactly is the meaning behind Km? What is the physiological importance of the Michelis constant? This is what we want to focus on in this lecture.