What is the measure of a kilometer?
The second order rate constant kcat/Km indicates the catalytic efficiency. of the enzyme: A direct measure of the efficiency of the enzyme in transforming Subst. kcat/Km combines: the effectiveness of transformation of bound product. the effectiveness of productive substrate binding.
- Kd, however, is the dissociation constant, and measures the dissociation of the substrate from the ES complex. Therefore, the larger Kd is, the less affinity the enzyme has for the substrate.
- The Ki is the concentration of inhibitor at which under saturating substrate conditions the reaction rate is half of the maximum reaction rate Vmax. A good inhibitor inhibits in the nanomolar range. Sometimes an inhibition in the lower micromolar range can still be acceptable. A Ki of 31 mM is simply bad.
- One manifestation of this is enzymes or receptors that have multiple binding sites where the affinity of the binding sites for a ligand is apparently increased, positive cooperativity, or decreased, negative cooperativity, upon the binding of a ligand to a binding site.
Updated: 16th October 2019