Question

Avidin binds biotin with a K_d of ~10⁻¹⁵ mol/L. A protein of interest can be covalently linked to biotin and subsequently isolated by incubating with beads coated with avidin. If the concentration of biotinylated protein is 10^-8 M at the beginning of the assay and the beads provided an excess of avidin-binding sites, then one could expect the beads to bind:

a. Less then half of the biotinylated protein will be bound to the beads.

b. Exactly one-half of the biotinylated protein will be bound to the beads.

c. More than one-half of the biotinylated protein will be bound to the beads.

Answer 1

As the beads in this case provides excess of avidin binding sites so definitely more that one half of the biotinylated protein will be bound to the beads. This is because the the in biology the interaction between the biotin and avidin is probably the strongest that is the affinity of their interaction is highest and the km value or the kd value is lowest. So it will bind more than one half of biotinylated protein.