I have calculated dissociation constant for an enzyme inhibitor (say A) which is about 500nM. The dissociation constant for similar inhibitor from other species (say B) is about 1.5microM. Based on dissociation constants which is more potent inhibitor, A or B? Also please suggest some good literature for basic understanding of association and dissociation constants particularly for enzyme-inhibitor reactions.
Binding affinity is the strength of the binding interaction between a single biomolecule (e.g. protein or DNA) to its ligand/binding partner (e.g. drug or inhibitor). Binding affinity is typically measured and reported by the equilibrium dissociation constant (KD), which is used to evaluate and rank order strengths of bimolecular interactions. The smaller the KD value, the greater the binding affinity of the ligand for its target. In your case A is more potent inhibitor, about 3 times stronger then B (1.5uM=1500nM).
Kd, Dissociation constant, tells you how well the ligand and protein are dissociating. So, its inversely proportional to affinity. In the example you gave, A is a better inhibitor.
You can look up for literature on enzyme kinetics. It should be there in every good biochemistry text book.
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