Protein A has a binding site for ligand X with a K_d of 10^-6 M. Protein B has a

Question

Protein A has a binding site for ligand X with a K_d of 10^-6 M. Protein B has a binding site for ligand X with a K_d of 10^-9 M. i) Which protein has a higher affinity for ligand X? Explain. ii) What is the fractional saturation (x) for each protein when [X] 10 M? (b) The protein LsrB binds a small molecule called autoinducer-2 (AI 2) with a 1:1 ratio. Half of the binding sites of LsrB are occupied when AI-2 is at a concentration of 10 M. At what concentration of AI-2 will 70% of the LsrB binding sites be occupied?

Explanation / Answer

PROTEIN A has binding site for ligand X with kd is 10^-6M

-the bigger the Kd --the smaller the Kd

-less affinity,-------------more affinity and tighter the binding

PROTEIN B HAS HIGHER AFFINITY FOR LIGAND X.

THE LOWER Kd INDICATES THAT PROTEIN B WILL BE HALF SATURATED WITH BOUND LIGAND X AT A MUCH LOWER CONCNETRATION OF X THAN WILL PROTEIN A.

BECAUSE Ka=1/Kd

protein A has Ka=10^6 M^-1

Protein B has Ka=10^9 M^-1

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