Km is the concentration of substrate at which half the active sites are filled.Thus,Km provides a measure of the substrate concentration required for significant catalysis to take place. 因为KM值是酶活性部位填充一半时底物浓度，所以可以提 供了测定底物浓度的手段。 For many enzymes,experimental evidence suggests that Km provides an approximation of substrate concentration in vivo. 对很多酶来讲，KM提供了体内可能的底物浓度。KM is the concentration of substrate at which half the active sites are filled. Thus, KM provides a measure of the substrate concentration required for significant catalysis to take place. 因为KM值是酶活性部位填充一半时底物浓度，所以可以提 供了测定底物浓度的手段。 For many enzymes, experimental evidence suggests that KM provides an approximation of substrate concentration in vivo. 对很多酶来讲， KM 提供了体内可能的底物浓度